
I am in the process of setting up a new crabitat (for newly adopted crabs, so I need to work fast!) and right now I'm in the process of shopping. Here's a list of what I already have to work with and what I'm planning to buy. I'd really appreciate it if anyone can take a look at my list and let me know if it sounds adequate or if I'm forgetting anything.

What I have:
30g long marineland aquarium (this is a slightly uncommon size: 36 x 13 x 16 inches) This tank is currently painted black on the outer back glass with acrylic gloss enamel paint. Will the heater placed on this glass be an issue? Should I scrape the paint off now? I'd rather not as I like having it as a background.
Glass lid
Basic LED light + timer for day/night simulation (and viewing!

Water dechlorinator (Prime and Tetra on hand)
Analog thermometers and hydrometer
Resin aquarium decorations for climbing and hiding These have been cleaned with baking soda and vinegar in the past & rinsed extensively, should be safe..?
An assortment of appropriate empty shells
Dishes/containers to use for food and water
(Other miscellaneous aquarium supplies such as airline tubing, suction cups, aquarium sealant, black plastic craft mesh, etc... basically I may have some useful things on hand already. I plant to get crafty with decor and climbing areas.)
Things I have and may possibly use:
Live plants! I have tiny plantlets from a retired betta tank: Anubias, Java fern, and the tiniest amount of moss. If these are crab-safe and I can grow these emersed in the crabitat I would like to do so! I also have some philodendron and pothos vine in the house which I could use but it will depend on space after other necessities are put in the tank.
What I'm planning to buy:
50lb bag of play sand Will I need more than one bag for a 6" depth in my tank?
Ecoearth to mix into substrate
Instant ocean salt mix (will use salt water for mixing the substrate + supply the crabs with a saltwater pool)
Ultratherm Undertank Heater (UTH)- 11"x35" Is this the appropriate size to use on my tank?
A thermostat I'm sure I need one but I really don't know what to get, please help!
Better-suited decor/dish items for food and water
Possibly a fountain or waterfall for the freshwater pool
More shells!
Thanks in advance!