Back to the whole GTA RP thing. Myself and Andrew (AndrewDibbs Yes) have experience in setting up servers that run FiveM. It's a little complicated but there is a lot of open source things to grab and it does not take long to set up a server. Myself I am on the biggest FiveM community, DOJRP. In my opinion the only way to get a decent community is to have a popular youtuber play on it. Having a public FiveM server is on the edge to say the least. There is tools out there to prevent people from abusing the shit out of the server such as the VMenu which you can basically customize to your liking.
FiveM isn't the worst thing ever, but don't expect it to have population instantly, you will need advertisement.