How much different is the Su-35 from the Su30MKI. Can AESA be retrofitted?
It’s not vastly “different” if you look at it from the point of view of upgradability. The SU-35 has a single pilot (can’t be replicated), more advanced fly-by-wire and use of composites and no canards (so its more agile) and has a more advanced PESA radar and uprated engines. Most of these, expect the number of crew and absence of canards, can be incorporated into the MKI or any other SU-30 variant.
You would probably want a two seater if you are looking at long-range missions, irrespective of what the Russians say about the SU-35’s automation.