@dionys19 GTA games only are difficult if we didn't mods for them before. If yes, we learned the essentials and an intuitive way to continue modding in the next GTA game.
Peds rigging continues at same difficulty (just is important the polycount and level complexity in shape to know the difficulty), shaders knowledge is new requirement for GTAV to put proper materials look (like traditional gray specular map not works like in the big percentage of other games, in GTA V materials are layered shaders by colors stored in specular maps), but can be learned researching vanilla peds values and textures patterns, same happens with ymt ped metadata. Vertex colors and LODs knowledge is essential for any model in any game, but LODs can be ignored as you want.
Vehicles rigging is more easy than GTA IV, not requires too much submeshes, values and components in hierarchy, the game engine can recognize vehicle properties and fill empty values automatically. Materials keeps traditional required skills and just flags knowledge can be a issue but researching in vanilla files can be acquired, same way for vertex colors for burn FX and deformable zones. Metadata edit can be tangled up for those who do not have patience or not understand well the vehicle's behavior in game, but can be learned taking note and doing tests without major difficulty. The tool knowledge is essential and Zmodeler keeps its confusing UI, but nothing impossible to learn about how to use it looking tutorials.
Map modding in GTA V can be more complex than before, with features like the layered materials used by vertex colors painting, there is required shaders knowledge or patience doing tests to get results and apply own settings. Just the tools not are plenty optimized and with all game map features working like in GTA IV or San Andreas, but actually are near to reach that goal.
Props and weapons continues in same difficulty, just the new material shaders can be difficult but can be learned researching vanilla models.
GTA San Andreas is a simple game engine, wihout major complexity in shaders and file settings and could be favorite for it by modding community.