General rule of thumb - CC, CC, provoke, spdup/spddown, hpburn/poison.

Personally I use Maulie, kimi, skarg, and two of pyth/bek/ratbomber depending on the wave.

Spd is by far the most important stat. Ideally 300+ on your spdup/down, and 250+ on everyone else. Acc second most important. Def/hp irrelevant for everyone but provoke.

I generally use ... Soulless , Mithrala , Cardiel , Elva#1(at 315 spd) and 5th slot open for countering specific floors ...but usually wukong or gnut#2

I cant get the total CC on champs that ruins floors(cupidus/venus , Siphi/rotos and Mortu) 

Im thinking of putting someone else instead of elva but when i do put a CC champ .. the team lacks heals or revive(since cardiel isnt one)

Keep Elva, she's important. She's your spdup, and the block debuffs doesn't hurt either. Keep Soulless, he's your provoke. Cardiel stays too because he just cheats.

For the last two spots you want hard CC. Stun/freeze/etc. Ragash is good as he provides a second spdup to make sure it stays perma active, and he brings stun. Yakarl is good because he has the aoe freeze and single-target freeze on both A1 and A2. If she's booked, Morrigaine is good too. No spddown is unfortunate, but c'est la vie. You could consider dropping Cardiel for someone who brings spddown.