Almost all land snails will be eating your plants, not much you can do about that.

You can use vinegar to remove hard water deposits but you may want to tear apart the whole tank so that you can make sure that you get all of the vinegar out.

I would just stick with isopods and springtails.

Most carnivorous plants that I know of wouldn't even survive in that kind of enviroment, you may want to ask Bill(Deranged Chipmunk) as he is the real plant expert

I hope this helps!

Lol looks like I need to type faster, everyone is stealing all of my answers :P