Ok, first off, there's a ton of great 'I'm new and need info' posts here, so I'd definitely do some searching and browsing in addition to the answers you get here.
I'm not even going to tackle most of your questions until we discuss lighting (mainly because I'm in no way a biotope expert so I can't tell you which plants to get)
You don't mention lighting levels at all, so I'm going to assume that you're using the lights that came with your tanks. If that's the case, you'll have less than 1 watt per gallon, which is low light, and only a few select plants will survive and thrive with that lighting. I think for the most part though, each tank biotope will need at least 2 watts per gallon, which gives you moderate lighting. If you find plants that require high light, you'll need 3+watts per gallon to keep them thriving. Some high light plants can grow slowly in 2wpg, but a lot of them just shrivel up and die.