with wife & 3g turned off, i assume you are accessing the Edge-equivalent network to AT&T here in the states. (unsure of exact network configuration from carriers in england) so your internet connection will still work. it will just be a lot slower than 3g or wifi.
as for the battery? well if you're on Edge and you have wifi & 3g turned off, your battery 'should' last longer. but if you are constantly fiddling with your iphone (running apps, email, games), then of course your battery will drain quickly. it doesn't seem to take much for me to be at 30% left by the time i come home from work.
if your battery drain becomes an issue, you might consider a battery power pack. there are many threads here on the forum discussing them. either way, enjoy your new iPhone!!