Im not the expert but I have 4 apple snails, anyway
1) My apple snails are always falling off things, its never done them any harm.
2) Quite the opposite of cats, they dont always land on their feet, but unlike tortoises they are able to right themselves.
3) Can't help you with breeding, mine are 'at it' for hours every day sometimes 3 of them at the same time, but I've not seen any of the eggs yet which are laid above the waterline.
4) The orange ones will only eat dead leaves whilst the striped ones can demolish a new plant in 4 - 5 days (in my tank anyway

)
5) The orange ones stay relatively small, but the striped ones can grow to the size of an apple (one of mine is about golf ball size)
Hope this helps, but when William gets home from school and has finished his homework

I'm sure he will be able to contribute more.