Haha no worries about it being long Now as for your questions:

1. The false bottom is usually used for keeping the soil from getting to wet and rotting, and I would personally just use a false bottom not the gravel.

2. As for the backgrounds I would use spray foam as it can be easier to get the shape you want but it really just depends on what you want.

3. Everyone that I know that has used great stuff in their enclosures was perfectly fine with their animals, as for applying sealant, you need to wait about a week or until it is fully cured. I wouldn't use acrylic paint or grout personally as it doesn't look very natural to me, and for sealing yes it will need to be sealed, I know Deranged Chipmunk uses titebond III mixed with cocofiber or a similar substrate. Again I would probably wait a week or until it is fully dried.

4. I know that moss paint can be used even though I haven't used it myself, but you usually just leave it alone until it starts growing then you mist it. And yes their is cleanup crews such as in aquariums, you can use isopods such as wood lice or/and you could use springtails which your frog will snack on if hungry

Oh and I just saw that this is for pacific chorus frogs, one thing they do like is lots of water they swim like crazy in it

I hope this helps!