More of my opinion.
start the game with 3 f17s, play until the first corvett is seen by radar."sir! this one is big, never seen anything like this. i dont think our current fighters have the firepower to bring one of these down with any reliability"
pop up a research screen to research not the new tech. of a fighter but to research what fighters available on earth could be best fitted with the biggest weapons to fight them.
could be a 1 day research for 10 scientists, then, after the research is done make the mig available to buy/build. buy would be best.
when the mig gets to the base it has the normal rearming and fueling time in base before it can be used.
first research at the beginning of the game could be extended radar range, wouldnt need to be much. or.
it could be better,more reliable radar penetration.*same range but better chance of detection* and again it wouldnt have to be much of a gain. "sir! we are getting eye witness reports of ufos planetwide but we seem to only get radar pings on aproximately 20% of them"
and i guess this makes my 4 cents worth.