Loudness depends on the switch.
I'd definitely go on youtube for sound tests on switches and pick ones you like.
Make sure to get prelubed or if you're building a keyboard yourself get a kit.
Everything from the chasis, key plastic, padding in the keyboard, and key switches have everything to do with how it sounds.
I have some painters tape and a peice of foam to absorb some sound, and make a "thockier" sound.
I built my first keyboard about 2 years ago? Was fun but tedious.
Milky yellows, manually lubed.
Some key cap set I found on amazon.
https://i.imgur.com/PHN0ubb.pngI did exactly that I think outemu switches were very comparable to all the premium super silent switches and I am more that happy how they sounded. I figured I might mod the keyboard further with fun key caps later but it will be a direct upgrade to the one I have.