Hi Luke,
I think a public website about climbable trees is not such a good idea. For starters, most municipalities prohibit tree climbing in parks due to liability issues, so publicizing where you are climbing is an invitation to a run-in with the law. You also mentioned potential tree damage issues, which is a real concern. Better to keep your climbing trees' locations private, to be shared only with responsible climbers that you know.
You've asked lots of questions about tree safety, which can't really be answered here on the Forums given the many factors that go into identifying safe and hazardous trees. Also, the climbing itself has inherent dangers due to improper technique, faulty or inappropriate gear, etc etc. I really urge you to get some training in technical (rope-and-saddle) tree climbing if you're going to do it. (We [TCI] offer an "online tree climbing course" in our webstore which includes our "Tree Climbing Basics" DVD for the practical training of setting ropes, knots, climbing, etc.; and it includes our online manual for all the safety, gear, weather, etc etc info. $85 bucks may just save your life.
Stay safe up there!!
Patty Jenkins
TCI Executive Director