One press will do everything expect most won't be big enough for 50 bmg- no worries.
Most dies are universal but if you find some that aren't many pressed have bushings / adapters to allow different dies to be used. Like lee breech lock system. No worries
If I were you, I'd buy a single stage press that's available and some dies that are available. You'll be limited these days and will take some time to get everything together, when you find an available die set for one of your desired cartridges I recommend ordering bullets asap, they're running a couple months + behind so there will be a wait. Then start hunting for primers, buy any you can at a decent price , if they aren't what you need trade them for what you want. You'll need to look hard for powder too, watch the "where are components available" thread and get what you can. Powder and primers if bought online have hazmat shipping charges ($30+), don't just order a $20 can of powder and pay $30 to have it shipped- make your order worth placing - it's expensive but cheaper in the long run.
Very first thing to buy is a reloading manual, I like Lyman but the others are good too.
Powder & brass can be purchased directly from the manufacturer and is often in stock when everyone else is out. Can sometimes be backordered too and then you just have to wait instead of just being out of luck.
If you live in a rural area you'll have an easier time finding components , if you live in the city or suburbs expect to do the majority of your buying online.
If you want cast bullets , I like Missouri bullet co.
If you need brass, check on starline site.
If you know what powder you want, check on hodgdons site.
Good luck, tough time to start. We're all hanging around blabbing about reloading over here and most don't mind helping.
Welcome to the high road