As a long-time Gentoo user, I can tell you that it’s perfectlly capable of producing both a useful gaming rig and a useful server, provided you have some idea of what you want to end up with.

Proprietary nvidia drivers should be straightforward enough: emerge nvidia-drivers and blacklist the nouveau module (or compile a custom kernel that doesn’t contain it). You’ll probably want to read what the Gentoo wiki has to say about Steam.

Good luck.

It has better specs than the 2008 laptop I retired last year (I was running Gentoo on that, but I don’t entirely recommend that unless you’re experienced with Gentoo and know what kind of setup to go with). Anyway, SNES emulation is less demanding than running a modern web browser, so your little beastie should be fine for that.