Yes definitely choose either the smaller rainbows OR the larger more robust species (you might make it work in a 2-3meter tank but I'd not try in anything smaller, the delicate "littles" seem to just fade away when kept in non-ideal situations)
As for fish #'s - they're like flowers, more aesthetically (to human perception) in odds
Choose 9,11,13 etc
You've skipped my favourite
Pseudomugil paskai
If the fish are stocked regularly, why not begin with 7-9 of each & then add more of your favourites
though if going this route, I'd add 2 groups of 7 at the start just to provide sufficient numbers
Of course, then repeat additions of new fish brings up the issue of quarantine (regardless of shop excellence)- can you fit an All In One Kit tank inside your cabinet? as hospital & quarantine & fry tank
Something in 35-50 litres (thinking of the Dennerle Scaper kits as they seem fairly economic, just confirm the lid as stressed rainbows are decided jumpers); a Spec 19 would work, low water volume but decent swimming length for these sized fish & the filter capacity is astounding (but would need to cover the cover re that long slit for light - I just use a plastic bin lid with rock or stymie the Cat Monster)
(Edge series tanks are much lower oxygen, not sure I'd use with stressed rainbows despite better closed top)