The tray isn’t that deep for a cham to swim, let alone drown. But external cage drainage is a must! Good job on pointing that out!I can't tell from the picture if the drainage tray has some screen/netting on top of it, but for the sake of safety, I would put something over the pot. Chameleons can't swim and it's easy for chams (as well as feeder insects) to drown. Better safe than sorry.
I say get rid of the standing water, it’s just a breeding ground for bacteria! It’d be hard to sanitize the Terra cotta because it’s so porous!
Get a substrate tray (rabbit ones from tractor supply work great), and layer egg crate/lighting diffuser to build up a false bottom (sturdier than zip-tying a base together), then add a moss mat or reptile carpet. Once it fills up siphon it out or empty it
Lighting diffuser is plastic, so use that, it builds up thicker layers easier than mesh
Any hardware store. Home Depot or Lowe’s
It all depends, just try different wattages until you get the right temp
