you'll be in the Shuttle class then! Great, welcome to Shuttle!
No you do not need a uniform! A week or so into training a guy will come and measure you etc etc, please don't get pleaded pants they are ugly! Business casual is appropraite, when you have been there for two weeks you will stop ironing too and not care.
You get your ID badge the 3rd day your there, so you can jumpseat home om the weekends!
you will be in STL longer than that probably 4 weeks.
Work out clothes if you plan on working out ( i forgot those), as far as everything else goes they provide you with everything books for class, jepps etc etc they give those to you, you might want to bring your FAR/AIM FAR/FC, flashcards. Flight safety gives you a bag to carry your books in, and some goodies.
There's a laundromat next to arby's that's in walking distance, some fastfood chains.
If it's driveable i would bring your car (but realize you will be everybody's driver and the DD). The hotel van won't take you further than 5 miles, but if you bribe the weekend guy that works at night ($5-10 bucks a person he will take you where ever you want to go that's reasonable.)
When you check into the hotel make sure you have reservations that are longer than a month (we got screwed.)
They serve breakfast at the hotel, waffles, oatmeal, muffins, fruit.
Flight Safety serves breakfast as well, cheerios, oatmeal and donuts, fruit. (that's why you bring your workout clothes). Both Flight Safety and the hotel are free of charge.
Depending on the sims (the 170 sim in STL is brand new and still has some flaws so they are running behind.) My class had to go to Montreal. You might go to Charlotte. You will have couple of days to several weeks of inbetween ground school and sim and IOE. Depends on circumstances though.

Goodluck, it's not too bad, chill and you'll be fine.
Will this work for you?