Ukrainians are already using some advanced anti aircraft, so training outside of Ukraine can be done, the people who normally operate these systems aren't IT professionals, manufacturers generally speaking, make these systems relatively easy to operate (i got this from my cousin who did 18 years in the RM's and our best friends whose DH was 12 years in 3 Para) Plus we would be training people who already operate various missile systems, not totally untrained folk
Fair enough, here's my POV after a couple of decades in HM Forces in a very much technical role, which for a while included training other people.
Give the Ukranians S300s with the same modification state/upgrade state as they have now and as long as they can integrate it with the rest of the air defence system they might well be OK on day one.
Anti-ship missiles - I'll leave to somebody else..
Fighters - supplying generic "MiGs" etc simply won't cut it...
You'd need to deliver an exact clone of whatever the Ukranians have in their Orbat right now, right down to weapons compatibility, cockpit layout and avionics fit if you are expecting Ukrainian pilots to jump straight in and fly combat sorties...if you can't produce a exact match you are either looking at months of retraining to get close to being combat effective in contested skies or your loss rate will be even more horrific than it probably has been.
FWIW handing over western tanks get a mention sometimes, so I'll stick this link in, it addresses not just tanks but the whole idea that the west can just chuck load of kit at the Ukrainians and thinking that's job done:
twitter.com/MarkHertling/status/1510341553520361472?ref_src=twsrc%5Etfw%7Ctwcamp%5Etweetembed%7Ctwterm%5E1510341553520361472%7Ctwgr%5E%7Ctwcon%5Es1_&ref_url=