hi mate the best ones to breed for a newcommer to breeding channa are either gachua or orinentals ,
personally i would go for orientals , purchace 4 to 5 in a 30inch standard tank or above , tropical temps ,prefer softer water but have been bred in a wide range of water , have bred in bare tanks and tanks with lots of vegitation ect . if you are interested i can give you the e-mail address of a guy who is selling juvies for around £6 each , one of the rarest snakeheads in the wild ,i will try and post some pics of mine over weekend , oh and the guy posts also .
to be honest rainbows arnt the easist to breed and must be kept at v.cool temps over winter then brought back on temp in summer if you want to breed them .
i also have channa pulchra juvies if you fancy sub-tropical species (kept at room temp year round ) but get to approx 12" and would need min 4ft tank . these will be around the £10 mark and be ready in a few week , or you could come and collect (iam only about 30 miles from you) and choose your own at around £8 each now ,and also see how ive set my tanks up ect
hope this helps cheers col