"I've now ended up with a 28cm rondeau in both ECI and thick copper (not a bad problem to have)" you're not alone. I've got one LeCreuset, one commerical anodized and one tinned copper version and I just got a sitram pan in similar size to use on the induction at the cabin... ;( . The anodized one is actually perfect I did not need the copper one at all I just "wanted it" there is no justification there and the ECI one as you said was just fine as well. The copper job is sweet though & I can leave it in my will LOL.

I have lots of stuff in lots of materials but the basics

1. a good size saute 11-12" with high sides - big enough to move stuff around/make a sauce and toss in pasta it to toss - also can "stir-fry" in lieu of a wok and for dishes like curries.
2. a stock pot around 8qt - big enough to poach a small chicken/make a decent batch of soup/boil spaghetti without gymnastics or breaking it
3. Sauce pan of decent quality - 3-4 quarts can do everything from heat a can of soup to make hollandaise or risotto
4. A heavy skillet or frying pan for searing steaks and chops - cast iron is common but these thick disk European jobs everybody on here loves also a good choice or carbon steel
5. A rondeau or large dutch oven for stove to oven use - braises, chillies, large casseroles

While ideally all of the cookware is oven safe and can double for roasting etc a small compliment of bakeware would round things out along with a colander/steaming basket and some good utensils I think I would have basically everything I needed for most tasks I take on.

PS never forget to have a wine bottle opener, a can opener and a cheese grater either.

"Using just a few pans makes me appreciate them even more. With these 13 pans, and a collection of oven roasting pans, I'm able to cook more or less anything I want."

for non cookware nerds 13 pans may seem like a lot LOL! I know I need to "cull the herd" and get rid of some redundancy. I don't have the patience to sell stuff but I need to relegate some pans to storage - too many makes for clutter and in the end the best pan for the job sometimes looses to closest at hand. There are probably 4 or 5 that I use for almost everything. I had done a good job of editing when I re-did the kitchen a few years ago but there has been creep.

First don't stress - new cookware day should be fun and exciting! not a source of trauma

There is no wrong path here - either of your solutions is workable .

Personally I don't like the hassle of selling things on the internet and I don't care about matching sets so I would go with return, buy what you need, and build up with the pans you find yourself lacking over time.

-for starters I would rather have a brazier/rondeau in place of the stockpot and 3qt saute pan (since you already have a stock pot and you want to keep/rebuy 11" skillet)

OTOH the Zwilling is a good set and a bit of redundancy wont't kill you. You may indeed find that some things come in handier than you thought they would. It's definitely not a bad set of pans for the money.

Most important - enjoy cooking and eating your food don't let this get you stressed out!

IMHO - there is a big leap that happens when trading up from absolute Junk cookware - (ie the blue enamelware I had in grad school) to good quality cookware (like nice department store name brand clad and disk stuff) and another (smaller) leap that happens when upgrading to super-premium cookware - thick copper or (fancy) Demeyer and Fissler SS products etc but the differences between those start to be splitting hairs to me when it comes to most all practical home cooking applications - if you have the right size/shape pan (of decent quality) for the job it should do what you need. My .02 buy what feels good in your hand and pleases your eye - there is joy in using a beautiful tool - but do not over think it. All the pans you mention are lovely high quality cookware that will serve you very well. Ferraris and Lamborghini's are both wicked fast.

If it takes a magnet it will likely heat up but this does not mean its a good idea to cook on anymore than it would be a good idea to cook on another heat source with a pan not meant for that use. You don't need $100 pans to play with an induction burner - take a magnet to a 2nd hand store (or your local big box discount retailer) and you should find a plethora of induction capable, functional, decent quality cookware. Most of the commercial SS branded stuff & celebrity chef wares will take a magnet and work fine. You should not need to spend more than $5 to $15 a pan. Make sure you take a magnet thought as same looking clad and disk bottom pans may or may not work.

my thoughts are if you are looking for oven to table bakeware/serveware then the ECI is a good choice but if you are looking to use as a saucepan on the stovetop and for searing/deglazing etc you will get better performance out of the Demeyere and it can still go in the oven and to the table. If I had to choose one it would be the Demeyere with the one caveat that if used as serveware it will retain less heat off the range - that seems like a small tradeoff. Either way you will enjoy the wide low versatile pan - one of my favorite size/shapes.

I was re-gifted one at xmas (thanks dad ;)) brought it up to my cabin where there is no oven, just a single induction hob and a microwave - I have played with it a handful of times. It definitely does not "fry" anything, it is more of a small convection oven - ie. ez-bake for adults . I find it useful so far in a kitchenette with no range hood - bacon for example cooks well - no smoke or splatter. Definitely a gadget that has limited applications but not useless. The main limitation is portion size - it is successful at making a protein OR a side dish for max 4 people - I have a hard time visioning preparing a whole meal or serving a larger group effectively I am not sure it has much use if you have a conventional oven but when it was 4 degrees out and a bit cold to grill out it came in handy. It's not in the "donate" pile yet. As a companion to a single hob range and serving a limited number of persons it is useful. I will keep experimenting with it. Ribs were a "meh" but they were fast and un-messy. "french fries" were tasty but more like oven baked not deep fried.

It's really sort of over the top gimmicky but I do love Franklin Fountain

http://www.franklinfountain.com/

If you are in for a bit of an adventure Little Babies in Fishtown is, well, interesting. Their Icecream is very good - oddly even the non-dairy options are excellent - but some of the oddball flavors are too much - Earl Grey Sriracha is great but Pizza is GROSS (imo). The scene is totally Hipsterdelphia.

http://www.littlebabysicecream.com/

Bassets in RTM is pretty classic

http://bassettsicecream.com/

Gotta put my .02 here

Tags are just not the same as boards - while they may technically yield a similar result they are conceptually different. There is an order of operations difference between tagging a post with a location after you have written it vs. starting a topic on a board. I remain unclear what the goal of eliminating regional boards was but they certainly could have co existed with tagging. Clearly this is a made decision and it will run its course but I do think it was incredibly disruptive for many posters especially those who had formed communities around area forums. Given the general disapproval of familiarity and off topic banter on CH perhaps I have my answer. I will ask if this was the solution for the area forums why not drop all of the different forums and have only tags? That seems the logical conclusion to this experiment.

"If it really is the case that a menu with a significant percentage of vegetarian items in a restaurant not specifically aimed at vegetarians will be a money-loser, then this would suggest that the proportion of people whose idea of a meal is fairly fixed on it being meat- or fish-based is so large that virtually any vegetarian dish will do worse pair-wise against virtually any meat-or fish-based alternative. That seems hard to believe"

Given that the options are of equal quality and cost I would not have a hard time believing that - IME most non vegetarians will not choose a vegetarian main the vast majority of time - even when choosing a main where the meat is not primary. like a pasta or salad dish, they still will choose the option with meat more often by a large margin. Admittedly this is based on my experience and not empirical data but I have always had a good number of vegetarian friends who were destined to dine out with carnivores so have dined in "mixed company" enough. I think you inclination to believe otherwise is where your original premise is running into challenges. This is not to say a vegetarian menu option cannot be as delicious and satisfying as a meat option but it is fairly rare in my experience to see a non vegetarian order a vegetarian menu item. Yes the veggie lasagne, vegan banh mi, or seitan tips (specialties of various local restaurants here) are lauded by customers and indeed delicious, well presented, and expertly prepared yet I only see vegetarian friends order them. I have tried them at buffet style spreads or bites off plates but still never have been inclined to order them when other choices were available.