I'd suggest ruining an entire roll of the shortest and cheapest film you can buy by practicing in the light of day. Practice by letting the entire roll dangle in front of you and begin to learn to fasten it securely to the reel. Once you get the feel try it with your eyes closed. Then begin the rolling process. Learn to feel the curved film engaging the reel. Then do it all over again with your eyes closed. Once you are comfortable with this then try it in the bag. It may prove easier without the dangling film which wont dangle because you will working on a table or counter top.
As far as bag size goes, I'd say bigger is better.
I hope I correctly understood your question,