A 50 - 60 inch full draw bow is a tricky customer! Try by all means but later you will appreciate what darksoul said to you. I'd start at 68 inches ntn.
You should be looking for straight grain primarily. The staves you talk about spliting funny can all be avoided from the start.
Get your head at the base of the tree and look directly up the bark. If the tree is growing with twisted (althought it may be plum straight overall) grain then the bark will also be spirrallled up the trunk. DO NOT CUT if you see this at all.
As for size of tree to cut, I wouldn't be going larger than 4 inch diameter. Trees around this size can be split in two. Try banging the first wedge in the middle of the length with smaller diameter stuff. Although don't get stuck thinking you have to get two staves out.....1 good one is a wholelot better than 2 pieces of firewood.
Look for trees that at first glance could be mistaken for telegraph poles
Seriously though the straightest tree makes the easiest to tiller bow. If your staves have humps/bumps/diferent profiles between the limbs etc it becomes magnitudes harder to get a great bow out than it is with a plum straight,untwisted stave.
Get something roughed out then post plenty of pictures. You will get great advice and once that first one is tillered properly you will have a better idea what you are trying to achieve.
Good luck!