It looks great so far!

Looks like your doing a lot more than I was when I first got my crab.
Seems like you have already pointed out the main features that you need to change like getting more substrate and a bigger tank.
Props to you for being so on task and researching everything you need to do to take care of your crab sooner than later, that's awesome!
The main thing I would just say is that maybe you can get deeper water bowls depending on how big your crab is. If your crab is about as big as the other shells you have in your tank, then yeah you definitely should get deeper bowls so your crabs have enough water and can bathe themselves if they want to. I think those water bowls are more for teensy tiny crabs. If you do have a teensy tiny crab though, then you are totally fine for now!
Also, you can raise the humidity by adding a certain tank decorations that hold in moisture. I had a volcanic rock of some sort I think, it was kind of porous, had a lot of holes in it, so it could keep the water in and keep the humidity in pretty well. Sorry, I don't have more information about this kind of rock, but if you look around you can probably find what I am talking about. I don't think you have room for one in your tank right now, but if you are upgrading your tank size, it might be an investment you might want to look into!
Lastly, I notice that you are using store bought hermit crab food, you might want to consider getting your food from other sources. Most hermit crab food from pet stores have copper sulfate and other harmful ingredients that actually are very harmful to hermit crabs. The hermit crab association has a list of safe food options if you want to look into that. If you still want to buy prepackaged food though that's fine, I would suggest just not getting it from a pet store and instead getting it from a website which specifically specializes in selling food for hermit crabs.
This video by CrabCentralStation goes over some of your options!
https://youtu.be/gG64EN9EWsg
Looks like you are doing great so far though! Keep up the great work

Hope you have a great day!