F-16s are going to be easier to train Ukrainian pilots on as they'll be converting from single seat ex-Soviet fighters to single seat NATO fighters. Probably quite a straight forward learning curve. You're quite right that ground crews will need training as well but if there's one thing that Ukraine has proven adept at it's taking NATO equipment and learning how to keep it working. They will also need secure bases, of course, but I've not seen any suggestion for a while that Russia has been able to undertake significant operations against UAF airbases or dispersal sites since the early phases of the war. They're all factors but none of these things are especially insurmountable.The biggest issues aren't just availability of aircraft. Rapid training of sufficient pilots and ground crews to service them will be vital and they need secure bases from which to fly.