I really like Vern's outlook on how much is enough. Unless you have your wood covered (I plan to have that project done this spring - will hold probably 20 cords), wood is usually usable for about 2 years so that should be the max stored outside uncovered.
I like free wood - means I don't have to cut mine. I have a chum who is in the tree trimming business and he brings me both the wood and the greens. The greens are used as mulch along the road etc., (makes great compost but takes a few years to degrade sufficiently). Doesn't matter what species, it all burns nicely and that is the main point. I have electric backup but we do not use it unless we are out of town during the winter. My youngest daughter will not make a fire - a phobia I guess, but that is my job anyways.