Setting up Q1 SP properly

Read this first:
https://www.quaddicted.com/quake/recommended_engines

Read this second (and please take their advice on emulating the software look, Quake's aesthetic is meant for unfiltered textures):
https://www.quaddicted.com/quake/configuration
Consider also using "r_lerpmodels 0" and "r_lerpmove 0" to have the FP weapon models and the monster movement animate as they originally did, and not in an overly smooth manner

Read this third (setting up the soundtrack, first address includes download links):
https://steamcommunity.com/sharedfiles/filedetails/?id=119489135
Alternatively (info only): http://quakespasm.sourceforge.net/music.htm

Read this fourth:
https://www.quaddicted.com/tools/quake_injector
With this, you can play 20 years' worth of fan content for Quake. There are some downright AMAZING map sets, and the community is still at it. Thousands of hours of classic FPS fun for free!