Every once in a while I have a post that is "not so grumpy" related. Even a blind mouse finds a piece of cheese every once in a while right?
For step by step well documented install examples I recommend highly Jeffrey Hunter and his idevelopment.info website ( Jeffrey Hunter ). He has a huge history of regular and RAC setups on various affordable pieces of hardware. Lots of things under various categories besides setup doc such as database administration, data guard, asm ... well just go over there and look around.
I am looking at doing some testing of 12c now ... been busy and well at the old job had some nice hardware available to use for testing infrastructure new versions etc.
Just found this resource for setting up under virtual box Linux 6.4 and 12c from a guy named Nikolay Manchev ... looks pretty good ... ( installing 12c in virtualbox ).