You need to start by deciding exactly what you want the game to do. You haven’t gotten far enough in that process.
Campaign: Sounds like you are asking about the “game loop.” Wait in lobby > game starts > meet conditions to win > back to lobby?
NPC: I actually recommend you start here. Split it into moving and shooting. Decide how you want the NPC to move, then try to do it. It’s much easier for us to help when you get stuck than before you know what you want.
There are a lot of good threads here you can search for every topic imaginable. Moving NPCs? Someone has written code for it. Read what they did, the errors they found, and how they solved it.
There are also good kits out there. I recommend Chrythm’s RPG kit for a nice entry level example of all component of a PvE game. I started there, and 6 months later, there’s nothing of the kit left, but I learned why things work the way they do.
Oh, campaign. Exactly what I was thinking. Although another name for it could be “Story Mode”, or “Singleplayer”. Whatever comes to mind.
To make a good campaign story game, always, always have in hand a storyline. Without a proper storyline you won’t have a good game. As it’s a campaign game, please do absolutely NOT use levels (level 1, 2…). In campaign, at least, every “mission” has a relation with the previous one(s). In levels, that’s not the case.
Suppose we’re making a WWII campaign. In the first mission you’re on the allied side and have to defend your base. The next mission must have relation to the previous one. For this context, it could be exploring the enemy base. Although it sounds off-topic, it’s better than just doing one different battle for each mission. Missions are supposed to be fun, and discover, investigate, explore, rather than doing the same things over and over.
All story games have voice. NPCs talk, which brings realism and gives a better ambient. However due to Roblox audio uploading costing Robux, unless you have a ton of it, I suggest you avoiding it.
One example of this is Entry Point. It may not be the greatest, but it’s an example of a campaign story FPS game.