That is what we need to know Afrikan, what rainbows to avoid, if any, or what not to mix. I am helping Joefish! set his tank up and he has joined our club. Are rainbows readily available in shops? Although I had a tank of them myself a few years ago they weren't bought from a shop and the breeder I got them from now lives overseas.
I had a big Melanotaenia of some sort. It was generally decided he was a cross between a boesemani and a lacustris but nobody was sure. He was in with neon dwarfs and never bothered them. I also had McCullochi and a couple of others but I can't remember what they were.
The CF1200 is probably overkill but bigger is better - when it comes to filtration I think.