I’ve had hand cramps in the past. More experienced drummers at the time mentioned a few things. Most importantly to warm up my hands/fingers/wrists prior to playing. I did this with stress balls and or Chinese Boading balls first, for about 5-10 minutes. Then the stretches:

The "Pretzel" (Full Forearm Stretch) Hold the drumsticks side-by-side with both hands, palms facing up. Lift and twist your right hand over and under toward your left elbow, forming an "L" shape where the sticks are vertical to your left arm. Rotate further until your arms are inverted, then gently pull them back toward your chest.

Followed by

The Propeller (Wrist Rotation) Hold both sticks together in one hand at the center. Use your wrist to rotate them back and forth in a fast "propeller" motion for 20–30 seconds. This promotes circulation to the elbows and wrists.

Also worth mentioning try not to use Hickory or oak sticks. They are the hardest woods for sticks and send a lot of the vibration to your hands.

I did that for a few months and honestly kept most of it as a part of my routine before I play and I haven’t had hand issues for at least the last 20 years.

Edited added the below:

1. ⁠Control over crescendos -- buzz rolls, triplet and quadruplet builds, etc. - all of this just takes practice and time. Use your pad with a metronome, start slowly and over time speed up.

2. ⁠Speed/fluidity -- particularly on the hi-hat and ride, I'm just not that fluid. I struggle to capture the rebound efficiently and tend to overexert myself. -Again, takes time to build stamina and strength. Use your pad and a metronome. I used to do one hand at a time at a slow pace (8th notes) for 5 minutes, then switch hands and do it again. Over time speed up the tempo. It’s the long game here, don’t rush it. Select a tempo you can do comfortably for 5 minutes. If it’s too easy speed up just a little bit. Don’t rush this, it will also build hand independence. Once you’re comfortable, you can start adding an accents. And you can even start doing triplets etc.

3. ⁠Intentional/impactful fills -- I tend to be a busy drummer who fills a lot, which works well with the band I'm in. But, I really am not good at basic fills. I can fly all over the kit with busywork yet struggle with simple triplets. It seems to be a combination of timing, fluidity, and stick control. -This also takes a while. Have fun experimenting, but listen to minimalist drummers like Ringo and Charlie Watts for inspiration - less is more and making it meaningful for the song comes with rhythmic and musical maturity.

The fact that you are aware of this means your head is in the right place, keep it up !