I really enjoyed my time in Mongolia before picking up the TS Express. UB is an ugly town but with huge energy and the people are some of the most welcoming I met anywhere.
You will find the city, because of the vast number of ex-pats working there in the mining industry, has lots if international restaurants selling pizza, hamburgers etc etc but there are some great local places too
Is a fun place, set up to raise money for local kids. Horse meat is a big feature and they did, if I remember rightly, very decent kushur.
Another place to try is the restaurant of the Chinggis Brewery. The beer is very good and the menu, although primarily aimed at German ex-pats, also has some interesting local dishes. The beer is some of the best and they also make a potent vodka
When you get out to the wilderness (one of the most beautiful places on earth) I am sure you will be offered airag, the fermented mare's milk. It's not particularly fun stuff, but it's rude not to accept.
You are going to have a fun time. I would love to go back