Now, hear me out. I know steamunlocked.net isn't the best source out there, but it seems to be the only site to actually preinstall your games. What I'm trying to say is, if you download gta sa from them you just get the game folder with the game executable and you're instantly able to just install mods without any setup. I say this because when I was in the same situation as you (i think about a year ago) , I couldn't get past the setups for gta sa, and this just worked. However, it might be worth it to take the game from any other source, and just install using the setup on either a windows vm, or another computer. Just know I've personally never had an issue with the files, but about 2 years ago (I think). The host they use for the files slowed down downloads.