you'd want one or 2 above it too, if using the 70 for premium taste, otherwise you are losing 1/2 your decent stuff 25-70u. as far as which one, you kinda have to do a run to see. some trichomes are differently sized than others. so, you'll read varying suggestions. Watch frenchy's youtube video part where he talks about which sizes he uses... if you want more go 25- ??, i do 25-120, and the stuff in my 120-220 isn't as good nor taste as good. very little was in my bags above, so i simplified after i saw the results. will be the same with dry ice as the anatomy of the plant you are sieving isn't changing, so i'd think you want the same sized sievs however they work, if differently.
i can't help with other part, sorry.