In reply to Sleepy_trucker:
It's nor unusual for bike shops to run a weekly group ride, so might be worth looking up some local shops and seeing if they do such a thing. Depending on the shop and the area though they might not always be beginner friendly.
I often spend hours obsessively poring over OS maps and satellite images to scope out routes. Bing maps is particularly good for this as you can flip between the two. There is always a risk of ending up somewhere less than ideal, so perhaps not the best idea till you build up your confidence.
There isn't really an equivalent to the likes of the UKC crag database for mountain biking, but with some patient searching yiu can often find some online route guides.
Edit: just to add good luck and hope you have fun! Also, as a bit of a bike snob it's really nice to hear you're taking the time to build up the bike yourself. Always think custom builds are an expression of the rider, and just buying some super expensive off the peg bike is a bit lacking in imagination (not that I don't understand why people go for this option before I get flamed). Hope that doesn't sound too pretentious, I just really like bikes!
Post edited at 21:45