[Notoriouz]

Would it be a good idea to add NPCs in SA-MP like those NPCs that you see in singleplayer? Or perhaps create a function for it? Probably AddDefaultNPC or something?

[Gammix]

Won't be a good idea to even have that much NPCs with that much of AI. SAMP's or GTA SA's NPC script is not meant for such things, should wait for a better update.

And no, since you create a function only when you want to use it more than once, generally.