Creating an quest npc addon troubles.

Hey thanks for checking out my thread. I am new here made an account just to post this, So the issuse I am running into is that I want to create an addon that is an npc with a custom player model (The player model part should be very easy to do), Now the hard part of this addon is that I need it to in some way once complete the whole quest line for a given NPC it “Unlocks” or whitelists players to that character to be played as a job, IE: You do a quest for a Rebel Medic only players that have beaten or completed the Rebel Medics entire quest line can be whitelisted and use the Rebel Medic as a job. It might help mentioning that this is going to be for a very indepth darkrp server that has a very detailed story mode for players to play while they do the normal darkrp and gives details behind certain eastereggs of the server. Last sentence I promise, I am somewhat new to lua coding i have ran many servers before but this will be the first actual addon i create and i have read some of the lua handbook but i just dont even know how to start this whole endeavor. Thank you for your time

You managed to not ask anything in the post, what is it you actually want?

I mean I did. I was asking where would I even start for something like this? and in the explanation of the white listing for completion of quests is something I dont know how to go about either.