glibc-eac is basically glibc, except with a few patches applied. Like literally just one additional .patch file. You can see that on the AUR listing, there is an additional patch called reenable DT, and the PKGBUILD applies this patch implying it’s the only thing that needs to be changed. And indeed, the original PKGBUILD differs in just that one patch, afaik. They even have the same version number (as you can see with pacman -Q glibc-eac and pacman -Ss glibc). This means as long as the custom glibc-eac does not get out of sync too much, it’s fine, as other packages usually don’t rely on an exact version - it can’t be guaranteed that the most recent version of something is installed all the time anyway.
As I see it, there’s glibc and glibc-locales. And for some reason you need to install glibc-eac-locales instead of just glibc-locales when using glibc-eac - I guess it’s because it’s a split package, which means multiple packages are built with the same source.
On the same note, you’ll also need the 32 bit version for steam things - basically just use the AUR manager of your choosing, search for glibc-eac and install everything that has a just-glibc equivalent already installed.

And on the topic of compiling: After installing LFS on a 14 yo Dell Latitude with Core 2 Duo (that thing could legally drink and fuck here in germany) I’m very patient and grateful for even my 5 2600 (6 cores). But it’s a nice experience to compile stuff on my E5-2680 (14 cores). And I’m looking forward to the 9 9950x (16 cores) :3