I would say that while you are working up to being fisted to stop kegals. You need to learn to do the opposite open up and relax. But once you do succeed feel free to resume kegals and be assured that you will never be loose.

Fisting should never ever cause pain, maybe a little discomfort but never pain. Just go slow to your goal!!

You've actually made a good deal of progress and its normal to get stuck with the tucking in of the thumb. There is a website fistforum.com that discusses nothing but and will have more tips on hand positioning and positions you can be in.

As for other things you can do to prepare is size play of course! Larger and larger dildos or objects that your in control of so you learn how things feel and how to relax etc.

Good luck!