Hardware
Is your computer powerful enough to run GTA 5 with the additional resources required to run a modded game? Without crashing, without texture loss, and with proper FPS?
Gaming in general takes adequate Computing Power and GTA 5, especially when modded, is no exception. PC hardware includes your GPU, CPU, System RAM, and available HDD storage.
If you're experiencing crashing or an infinite loading loop at launch, it could be that your PC hardware is not powerful enough to meet requirements for modding. This is particularly true for laptops. For example, if you are running Windows 7 on a laptop with integrated graphics go real easy on the type and quantity of mods you install.
If you can't upgrade your components or the PC itself, again add mods one by one and see if you can handle them before adding others.
Ensure your PC at least meets the Recommended System Requirements below for GTA 5. If you are installing many mods, you will often need to exceed those requirements.
OS: Windows 8.1 64 Bit, Windows 8 64 Bit, Windows 7 64 Bit Service Pack 1
Processor: Intel Core i5 3470 @ 3.2GHZ (4 CPUs) / AMD X8 FX-8350 @ 4GHZ (8 CPUs)
Memory: 8GB
Video Card: NVIDIA GTX 660 2GB / AMD HD7870 2GB
Sound Card: 100% DirectX 10 compatible
HDD Space: 65GB
One word of caution. Even with a Super Computer, you can't install an infinite number of mods. The game will not be able to handle it, it was never designed to be modded in the first place.