You're naturally going to find a lot of people that are more well off than you, but also the opposite way round too, but if you go for the most expensive halls, you'll have people whos parents can afford it etc, but it's the same with any university.
The Vale isn't too long a walk from the City Centre, half hour max, but I've never done that. There are plenty of bus routes that'll get you into the City Centre, you'll not have to worry too much about getting there. There's also the train station too.
This link is the vale to the other end of Broad Street, the main pubs/clubs area of Birmingham, though not limited to it:
http://maps.google.co.uk/maps?saddr...52.465527,-1.914368&spn=0.02327,0.058537&om=1
Rooms are generally organised in flats of 6-8 I believe, depends on where you are again, and there's the chance you'll find some people on your course, but depends on how you fill out your accomodation form.
What your flat mates are like however, can range from anything, they may turn out to be your best mates in the world and you end up living with them in a house in Selly Oak the following year, but you may also get a load of idiots that don't match your personality at all. I think it'll depend on how you fill your form out again as to what kind of people you'll be living with, or if it's mixed with girls and guys etc.
You'll probably get on well with a lot of people if you're the kind of person that doesn't mind getting drunk a lot, but remember, your halls aren't going to hold you back. There are so many societies that you can join and make friends with, and the advantages with socieites, everybody has a similar interest, like go karting (me

) or music societies like RockSoc etc. Then you've got the people on your course, and likely the Elec Eng society will do lots of social events to get everybody knowing each other and all that. Plus you've got sports teams too.
I'm sorry I can't help you with which to choose, but wherever you end up, as long as you go out willing to make new friends and meet new people, and actively you should have a great year.