Lived in Taiwan so I get cheap PCBs which are pre-solder with diodes from taobao.I simply solder on switches(which is kinda easy), assemble stabilizers, and put it into the case.
I found the hard part is to modify small things so it feels good(springs, stabilizers, case, etc...)
The first custom made keyboard may not be such satisfying, but after learning experiences my second custom keyboard which I am currently using is quite satisfying.