Quests are not plugins. It's not like a Skyrim mod where you just download an existing quest, plug it into your game, and suddenly new content exists.
You have to make the quest yourself.
I don't know what kind of plugins you are looking for as there are literally countless numbers of plugins available here, on itch, git, and on personal websites by developers from all across the world.
It might be a good idea to plan your game a little bit and see what you need, and then put in requests for specific types of plugins to help you achieve what you want.
Broadly speaking, I suppose whatever VS's free pack offers is a good starting place.
I'd advise against adding plugins just "to spice up your game". That's how you end up with an incoherent mess of a game with too much scope creep. You really do not need 800+ plugins that add nothing to your game. Instead, consider figuring out what exactly it is you want to do with your game, and then look for plugins that can help you achieve that.
Even if game dev was Like Game Modding, I would hope you wouldn't just chuck any random Custom Content in just for the virtue of having it. That's how you break saves and make the game not boot anymore.
I digress. Yeah you'll have to make your own quests with the Plugin, and only you can speak what you want your game to be/do. There's a million Plugins, some graphical, some centering around gameplay/mechanics, all of which need a little work and tweaking to accomplish what you want. If you need help finding something, we can maybe point you in the right direction but that's it.
Yknow what? Im seriously considering recruiting a manager to oversee my games development.
Because I cannot focus or complete these tasks by myself. I need someone to give me orders, without having them be my boss.