1) Drainage: what I do is quite simple, add a literal drain. A simple hole saw of the appropriate size for your drain (I use bathroom sink drains - 1-3/4") and Bob's your uncle. A decent drill and hole saw WILL go through just about any material. If for some reason you're using something tougher than,say, 1/4" of steel, you may not be able to go this route. Otherwise, a little bit of screen mesh and silicone sealant and you're set. Unless you're going with....
Bioactive will manage poop to a degree. I still grab out bigger clumps, but I know they will poo somewhere i don't see. Adding springtails and isopods is fairly simple and can be combined with either the above drainage method or using a 3/4" PVC pipe with holes for access to the drainage layer and using 1/4" tubing to siphon out excess water. (I did my gecko this way and use an old "monsoon" mister pump to drain it. Almost any pump will do the trick, simply add an air stone to the end of your siphon tubing to prevent grabbing debris!)
2) Food containment: I hand feed most of my guys and gals, that way I know what they eat and when they eat. That being said, I hear good things about "The Shooting Gallery" (Rainbow mealworms sells them online).
3/4) I havent done this myself but I've been gathering the supplies through work and plan to be doing it soon. You can use "Great Stuff" and one of the "egg crate" style light fixtures and add plant pots. Browse the enclosures thread and you can see some AWESOME inspiration! Otherwise, I personally use LOTS of cork Garland mood/sheet moss. I then plant misc plants throughout that are appropriate size for the cage. I also utilize hanging plants like orchids and bromeliads and airplanes.
5) sorta covered above, but I use a money tree or hibiscus as my "feature" tree, flukers fake vines as pathways, pothos, and a myriad of other plants. Just watch for anything spikey, pointed (for eyes), toxic, or has sap.
6) Wood for the cage itself, or decor? I use some stuff off Amazon that's cheap - just read the reviews as much of it is super tiny! Otherwise, I grab stuff from outdoors and soak it then bake it - if necessary. I also use lots of flukers vines as they're super cheap on amazon.
Here's my latest for my little gecko:
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And here's my first/best of my builds - until the end of January: [dont have any full shots at the moment, but here are some partials]
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The wood he's on is driftwood from the local flea market. Cost me $5 and its shaped sort of in an S. I had to cut it a bit, but was perfect for his cage. It's also grown in a ton since I first built it.
I'll also add that there are MANY ways to do things. Even now I plan to scrap every cage I've built when I move and redo them all with my things I've thought of and learned through posts like these.
Best wises!