Thank you, Greg and Nozzer66!
Allright, so I've installed all STEP:Core and some STEP:Extended Mods, along with Alternate Start - Live another Life, Immersive Horses, Hunterborn, Frostfall + Campfire, Skyrim Immersive Creatures, Deadly Dragons and The Dragon Engine. The only things I did not install were: the High Res DLC, the Unofficial High Resolution Patch and STEP Optimized Vanilla Textures (I know they are core, but on Tony's Mod page, unless I read wrong, they are not needed when installing his Textures using the High Res Version)
However, now when I try to start a game, it begins loading normally, then the screen stays black, with ambient sound. Only way to get out is by using CTRL, ALT and DEL and Log off (Task Manager won't work). Are there some ini changes I need to make since I don't have the HighRes DLC and stuff?