No it'll never be possibe to use a pirated version, we don't want to get shut down, plus personally it's a pain in the ass to troubleshoot pirated issues as they get different issues compared to normal versions. Correct, Steam or Social club work fine, if you can purchase it and redeem it on Steam or inside Rockstar, then it works.
You can join Discord and look through the media section, you can look through our announcement threads, or you can probably lookup videos on youtube.
Built into RageMP? No, but there's a resource someone made if you want to run a server with a map editor, otherwise you'd just go into singleplayer and do that yourself.
I don't think there's a maximum number of slots, it's just however many your server can handle, and players don't take up much resources. Same with max vehicles or objects, but there is a maximum amount of how many vehicles can be spawned within the stream range. The limit I believe is 128 so if there's more than 128 vehicles in your view, some will start to disappear, this is a GTA V thing and nothing to do with the mod.
I don't think there are any 'finished and ready to go' gamemodes, they take a long time to make so you could imagine how many hours someone has to put in to make one completely working. I'm sure there are some that are nearly complete though.
Not sure what you mean by this.
That's more up to you, there's nothing RageMP can tell you what to do for your own community. I'm not sure what advice you might want.
Yes we have Linux server files, if you're using the bridge though (C# code) you'll probably run into some issues running it on Linux at the moment, this could improve going into the future but keep that in mind for now if you're going to be testing using C# code.
No not right now, just don't announce it on the master list and nobody will join. Otherwise make a quick whitelist script or make a quick login panel with no registration on it.