Online play is pretty straight forward once you know how. Not sure if the tanks have movement replication built in though. I know characters do, but generic pawns don’t. So that’s the biggest issue from my point of view. I’d assume the vehicles do since most vehicle games would be multiplayer.
The rest is pretty straight forward for pretty much all multiplayer games. You should probably make a basic multiplayer game before you start trying to convert a single player game. A single player game is basically a multiplayer game without other people. But a Multiplayer game is SO MUCH more than a single player game and converting a single player game to multiplayer is a HUGE undertaking. So mucking around with something basic is the best bet. Learn it in its most basic form before you start cluttering it with all the cool stuff.