A few more things about the Arcane Dimensions mod:
You should get both the base
Arcane Dimensions mod and also its
"patch 2". (There was a "patch 1" before this, but you can ignore that; patch 2 completely supersedes/replaces patch 1.) The recommended way to install is to first install the Arcane Dimensions mod in some mod folder, then copy the files/directories from patch 2 into that mod folder. The patch will add some new files and also replace some files.
The recommended Quake engine is
Quakespasm version 0.91.0 (or better). That's the Jan 18 release of Quakespasm, so if you downloaded Quakespasm before then, you'll need to grab the latest version. I think it's also been said that
Fitzquake Mark V can run the mod. Once you have applied "patch 2", you can also choose to use
DarkPlaces. Or, if you really like the palettized-color look of a software renderer, you can use
qbism Super8 or the "winquake" variant of Fitzquake Mark V.
The mod is pretty memory-hungry, so broadly it's a good idea to use command-line arguments like "-heapsize 256000 -zone 4096" when launching it. (That's not necessary though if you're using a new enough version of Quakespasm, since QS uses large heapsize and zone values by default.)
Some info/discussion is over at the func_msgboard thread:
http://www.celephais.net/board/view_thread.php?id=61270