I am not sure if the PAK-FA is a very good investment. There have been too many articles claiming that IAF doesn't like its stealth features as well as engines/radar . While the Su-55 aka FGFA is going to be different, how different could its airframe be? After all shaping is far too important for radar evasion. IMO Iran should probably look out for KF-X or TF-X. Those will atleast have a chance of proper ToT unlike the Russians who will give screwdriver tech after double-charging and much delays.
And for Ind-Rus collaboration, well, after cold-war ended India financed and bought a lot of Russian stuff, so there was and had always been a lot of mutual trust, viz why they offered us a 50:50 partnership in FGFA in the first place (apart from money
) and money cannot buy this trust.