AC questions for the experts

I have a few questions regarding AC. I went to buy a 30lb 134A and found out you now need to have an EPA 609 cert to buy, at least in MD....probably all states? Anyways, just curious how hard the test is and what kind of questions to expect. The test is open book and no time limit but the "manual (online)" is massive. I plan on buying 3-4 jugs of 134 to hoard for when they ban it eventually.
Next questions are about the factory AC in my 71 swinger. It still has some gas in the system so im thinking it will work with a recharge. So to change over to 134 I would be looking at a complete flush, new drier, new expansion valve and oil. I am aware that the 134 wont like these old hoses but if I have to top the system off here and there that is fine. Am I forgetting anything here?
Last question is just an odd thought I had. I have a new sealed 30lb of R22. Can this be used in the R12 system? If so is the conversion process the same? Any benefit over the R134?