This was my first time properly playing Arma 3 after I bought it, it's great.
My only issue with regular Chernarus is that it's from arma 2 and is pretty outdated, I wanna try Chernarus 2020 I believe it's called.
Hell yeah!
Try out Overthrow, similar to antistasi, but has a lot of different interesting mechanics.
As for maps - cherno is still one of the best modded maps unfortunately, its being currently ported to Reforger as well. In the past ive played on many servers also on Takistan, but if you have DLCs Livionia, and Tanoa are really fun for antistasi, Malden as well.
As for gamemodes - there are even roleplays, only thing you need to know there is how to say "hands up or die", you meet someone every 1-2hours, and if you do, they usually want to do horrible things to you.
There are fun modded RP servers, using custom maps as well, but to play theese you need to really want to, as the performance is shit, and you need to learn a bible of rules by heart. They also tend to want you to download like 40-60GB modpacks, but as you already play modded arma, you know whats that about. (I used to have a disk partition of 300gb called ARMA on my pc)
If you are not familiar with the original launcher to the game, you can use A3Launcher - its still pretty decent when it comes to connecting to modded servers.