I've been vegetarian for all of my 29 years—and cooking since i was 16. My observations on this thread...
—Absolutely agree that vegetarians need less kitchen space than carnivores. I haven't analyzed why that is, just that it is.
—I cook for 1-2 people and my three most used pieces are: 3.5 qt Le Creuset Dutch oven; 6 inch (tiny!) Le Creuset skillet for tempering Indian food; and 11" Le Creuset square grill pan. I cook mostly grilled veggies, curries, lentils, tofu, rice and pasta.
—I have a full-time job and cook fresh everyday. I pack my lunch and cook dinner during the work week. On Sundays I prep food (cut vegetables, portion ingredients, etc.) for the week ahead. It's not a question of time, but of priorities.
—I still recommend the Le Creuset 5.5 qt. Dutch oven for dinner parties, holidays and potlucks. Great to bake bread, too.

Obviously, I'm a Le Creuset fan. Whatever your brand of choice, however, the above are my size recommendations for cooking vegetarian food for 1-2 people.

i disagree with most commenters here who advocate for the "rainbow color" approach. (do you want your kitchen looking like a rainbow?!) it looks so good when you have a LC collection in 1 or 2 colors. i say find a color you love and buy a starter set. later pick an accent color and again buy a few pieces at once. try to stick to the 1 or 2 colors as time passes by adding to your collection from the 2nd hand market. some LC colors clash with each other, so i advocate for a more curated approach. my friend has a black and white LC collection that is stunning. mine is cobalt and dijon. you can have stand-alone pieces, but it looks lovely to have a theme!

black and white is clean and sleek. i have dijon, cobalt and flame. i adore each color, but it gets "too colorful" when i use them together (admittedly rarely). i've moved around a lot. while cobalt matches every interior, dijon and flame are sometimes too bright. if i could go back and start my LC collection i would get every piece in either white or cobalt.

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my Le Creuset collection:

in DIJON:
5 1/2 qt. round Dutch oven
2 1/4 qt. saucier
10 1/4" square grill
8"x11" roaster
in COBALT:
10 2/3" crepe pan
3 1/2 qt. round Dutch oven
1 1/4 qt. saucepan with lid
in FLAME:
fondue set
1 3/4 qt. saucepan with lid

COBALT! it is discontinued now (2017) :( it's a medium blue with the loveliest purple tinge. the gradient is especially nice. i feel so calm and peaceful looking at it. it's gender neutral and neither a dull nor bright LC color. i've moved a lot and this is the color that goes with all interiors. i also have several pieces in DIJON, a mild, mustard-y yellow that brightens any kitchen without being garish. i love the color, but it has clashed in certain kitchens i lived in (rented homes, so i couldn't make changes). i have a couple of smaller pieces in FLAME because it's the bold, signature color. i have stoneware in a variety of colors. the one color i might get if i could go back and purchase my LC all over again is WHITE. white makes any space looks larger, cleaner and more pure. in a busy kitchen that is something always welcome.

DIJON (yellow) ! ! ! Everyone goes for Flame (orange). I dined at the home of my interior decorator friend, who laid out her table with Kate Spade dinnerware from the Gramercy Park line (multi-colored), accented with several pieces of LC in Dijon. The Kate Spade was gorgeous, but the LC in Dijon simply made the table! The particular shade of mustard yellow was so cheerful and elegant (yellow is rarely elegant). I strongly recommend LC in Dijon with smaller accents in Flame and Caribbean (turquoise blue). This is an unbeatable combination.

I have:
3 large pieces in Dijon (yellow)
1 small Fondue pot in Flame (orange)
stoneware accents in Caribbean (turquoise blue)