Fresh or does previously frozen work just as good?
I dont think anyone can say with certainty that frozen roe works exactly as good as fresh, but if it doesnt, it's got to be close. Every good roe fisherman I know uses frozen with confidence and has plenty of success.
Even if frozen is marginally less effective, it's simply not worth worrying about IMHO. The convenience of being able to use and re-use frozen roe far outweighs a few percentage points of effectiveness (if that)
Of course it presumes the frozen has been stored properly and not freezer burned, dried out etc. I have used vacuum packed cured roe that is several years old and it still looks great IMHO
As for species, I think they all work equally well or close to it (except for sockeye, which I have never tried). I prefer spring or chum because I use sacs and those are easier to tie with, but will use any species roe with full confidence. If I am getting outfished, I will wager that it's due to some other factor that's the overwhelming difference other than species of roe.