Re SFI:
Currently the TRTO is training FOs for SFIs on the fixed base sims (both Airbus and Boeing). If you have to be an seniour FO to do it, I'm not shure, but I think not.
As for getting your SFI rating before comming here - do not bother. Although a plus in your CV, they'll give you a full training here even if you've been a full-fleged TRE in you previous life.
Cheers!
H.L.