Doing it on your own?  Does not sound too feasible really.   If you have solid skills with aluminum, SS and steel; that is good enough to get a shot in a repair station or OEM.   Learning exotics on the job like Hastelloys, inconels etc. is not a real stretch.  I reckon the hardest part is some jobs want you to qualify down to ridiculously thin materials, that is where I have seen most guys struggle a bit.   Aerospace positions typically have good working conditions, reasonable working pace (they want you to be careful) and decent pay and bennies.  Plus you may have opportunities to learn how to operate e-beam welders or CNC equipment.    Problem is those positions can be rare and hard to get.  Right now is not a great time....but if you look hard enough there are some out there.   Lockheed Martin is looking for the right guy in Marietta right now, it is a shift job.   Other folks on here I am sure could give you some solid advice about it.

I think Tommy said it right.

Understanding and having good competence with Aluminum, stainless and plain carbon steel is what you will need to get in the door.

Learning... work on thin to thick fillets..  300 series stainless is fine.   .040 to .090  Tee joints with no burn thru on the thinner member.   Also.. Weld pop cans together to practice on the aluminum... When you get good at that.. go to the Tee joints.. It will save you considerable coin.

Understand argon backups and print reading.

The "myriad alloys"  for the most part have great similarities and once you are hired you will have training and more importantly class 1 repair doccuments that *should* instruct you on important differences in pre-heat, surface prep. etc. that sometimes come with exotics.