The only way to acquire the maniplative welding skills is to do it.Most methods are similar but slightly different.
Certain exotic steels such as HY -80,T1, Manteen etc require slightly different methods but most people will never have the need to ever weld these steels.It has been decades since I have .
Regarding the plasma cutters,I have cut 1" cast iron with one nearly as cleanly as with a saw.The thing about a plasma machine is the fact they will cut about anything ,whereas a torch is limited to steel,no cast,no stainless.
Aluminum welding is a pain in the butt for me,it doesn't change color much as it melts and my welds look terrible.
I never really checked it out but I don't doubt there may be some help on the internet with welding questions.
In my tons of equipment,I have no MIG no TIG but I do have two engine driven welders,4 electric machines and 4 sets of torchs.That's what happens if you hold your hand up too long at an auction sale.