A few days ago, I was looking for GTA 5 mods as I have been playing GTA 5 for months and to be honest the base game has a huge lack of side activities to do.
The mod I found was Gang and Turf Mod which is developed to gta5 mods user lucasvinbr.
The mod works like a more of advanced version of GTA san address gangs, where manage a gang and its related territories. Most of the mods game play elements envoy around protecting your territories from rival gangs.
A word of warning: I noticed the gang back up system (not in game back but in getting help in fights) can be pretty buggy especially with vehicles, so I would suggest getting back up before you get into a fight.
Link to mod: https://www.gta5-mods.com/scripts/gang-and-turf-mod