For the ankle issue:

Do your research and get a good set of pedals and shoes that can be tension adjusted to allow you to (once you are used to them) get in and out quickly and easily. Shimano pedals have a tension adjust, but many people also recommend Speedplay pedals for people with knee and other lower leg issues. Your should should be able to help you with this.

Then just practice practice practice. I started indoors, in a door frame, while watching TV. In, out, in, out, in, out. I've had a whopping 2 or 3 clipless related falls, all on the mountain bike, and most involving mud/rocks in the locking mechanism.

I don't see them as dangerous. At worst you are going to fall over at 1 mph and skin your elbow. Maybe stay on low traffic roads until you are confident with them, simply to avoid laying down in front of a car (which would likely be stopped anyway, but sometimes it's hard to unclip once you are down). But really, the mechanisms, especially when set on low tension, are very good at releasing at any "panic" type movement.

A good set of pedals and shoes will vastly improve your foot comfort on longer rides, and have the added benefits of at least slightly better efficiency, so well worth the investment and learning curve.