Typically, you'll want an equal amount of buffs and scorpions so that none of the cards are completely worthless.
Also, what Chapuz said. For neurotoxin, you don't really want to rush, since that ruins the point of using neurotoxin. Neurotoxin is more of a longterm effect that gets stronger overtime, so you'll want to take advantage of that.
I'd suggest maybe a few RTs for more neurotoxin, Sundials are good too.
I think for a Nova-powered neurotoxin rainbow, Fog Shield is probably your best bet.
SoSacs would be a good addition, although it would ruin the point of the rainbow since it drains all non Death quanta.