I've just finished my first year at Warwick, so I'll share a few things I've learned. I stayed in Cryfield (not Cryfield Village - that's still being built), which has lots of people sharing a bathroom and kitchen. On my floor, there are 20 people sharing 4 toilets, 3 showers, and 2 kitchens. I have never had to wait for a shower, and only once for the toilet. Having 10 people in a kitchen sounds hectic, but it's actually brilliant. You'll spend a lot of time in your kitchen, so the more people in it the greater the chance of finding good friends. I highly recommend choosing halls with large kitchens.
I wouldn't worry about walking distances too much. You'll never need to walk more than 20 minutes to get anywhere, including Westwood and Cannon Park. In regards to Cannon Park, this is where most people do their shopping. There's an Aldi, a Tesco, an Iceland and a Wilko and Boots, so there's everything you need. I only buy small things at Rootes, when I can't be bothered walking to Aldi for it, like bread and milk. I'm told it has an excellent Chinese food aisle, but as I'm not Chinese, it means nothing to me.
Cryfield is the shorter let, so you're required to clear your things out at Easter. HOWEVER, they only want the rooms cleared if they're going to house people visiting for conferences. If there's no need, you don't have to clear everything out, which was the case for me. You can't get in over the holiday, but you can leave all your stuff there.
I don't think you're interested in en suite, but to anyone reading, really think about whether it's worth another £2,000 or whatever. You probably share a bathroom at home, it's no different.