Okay, first of all, I'm not a doctor, and I don't know anything about the extremity of your hand conditions. I would suggest, before doing ANYTHING, going to your doctor and asking them about the potential stress that high input-per-second gaming might have on your hands and what they suggest, exactly. Don't ruin your body. That's dumb. It's a game. It's competitive, but competition should be fun, not physically scarring.
That being said, there are a lot of ways to speed up your fingers. The most important one is just playing the game. The more you repeat the motions of short hopping, l canceling, wavedashing, etc., the more efficiently you'll be able to execute those motions. Muscle memory is a powerful thing. From the perspective of a pianist, I've found that the best way to play quickly is to practice slowly. This may sound strange, but if you practice a technique as slow as possible, and gradually begin to speed it up, you'll have MUCH more control of precise tempo and technique than you would have by just mashing buttons as quickly as possible. Speed is all about comfort. Don't try to play in a way that makes you uncomfortable- you'll just sd off the side, lol.
Tldr; just be patient and play the game. It comes with time.
Also, if you have hand problems, I suggest thinking about button presses that minimize effort. For example, if I need to do a super fast Fair with Marth so I can get a double Fair in one short hop, rather than causing strain by trying to move my thumb from x to the c stick as fast as possible, I'll just short hop with tap jump and have my thumb already on the c stick, ready to go.
Try not to squeeze your controller to death. Think about gliding your fingers from one press to the next with as little effort as possible. This allows you to play longer and has an added bonus of extra precision.
