/vr/ - Retro Games

So, I want to make my own game/total conversion, the game itself is still just in conception, but there is a problem that I think I have to solve before continuing, what engine should I use? I've considered the Doom one, I have experience in it and it isn't as complex as Build, but I really, really want to try out 3D, so I'm still considering either IDTech 2/Quake 1 engine or GoldSrc.

The problem I have with those two last engines is that the only experience I have with those is just mapping. How hard is it to make mods compared to doom? And I'm not talking about modelling/animating, I have those covered, I'm talking about coding. In Doom you can make custom enemies and weapons in a relatively easy way nowdays, but what about in Quake? I find very little information about that and the very few cases I find anything related to Quake custom enemies, for example, are just demonstration videos like this one https://www.youtube.com/watch?v=YRMIzzZ13_E
How hard it is? Any of you have experience in modding quake beyond mapping? Care to share some stories and tips? I want to cover everything in my mod, I want to know if I want to make hub maps, how to make weapons, enemies, and in the most extreme cases, menus, like dialog boxes, inventory, etc.

TLDR, What engine should I use for a medieval themed game? Doom, Quake, Build or GoldScr? I really wanted to experiment with Quake but is so foreign to me that I don't even know how to start, or even start at all.