gentoo stage 1 is still possible, but not recommended, and the documentation is probably a bit hidden. but there is no functional difference if you do a stage 3 and a world rebuild, which is the recommended way.
the problem with gentoo is (and i say this as a former gentoo dev and enthusiast) that there is a lot missing on the audio side. last i looked (about a year ago) there was no ebuild for vcv rack, and a lot of other relevant packages were spottily available and maintained. i was thinking of becoming an active contributor again, but decided it would take too much time that i would rather spend on making music. there is no structural way in which packages get maintained in gentoo. you are dependent on the interest of individual volunteer devs, who come and go, or you need to learn how to do it yourself.