infinity.
depends on the detail, size, materials, meshes … etc etc. 32 gee-bees is good. start there. 16 will hurt a little. you should be ok with 16 if you are only doing 1 or 2 chunks, depending whats on them.
Honestly - by the sounds of it, you need to learn Unreal before jumping to something like multiplayer games. A simple single player based from other things from the “learn” section will do you right. I started working with Unreal (the game) and then later moved to mods for ARK … and now im on my own projects. Its been a less-then-exciting path, but, i cant imagine starting with the biggest, most complicated task this engine (or any) has to offer.
I cant imagine coming to a game engine and saying “guys, i want to make something like world of warcraft, can i do it with 3 people and 0 experience?”. OMG my head would explode lol … much … like … your teams will when your about 2 years into it and about 10% done … not trying to be a downer here, but, its seriously a massive task.
Also the cost is insane. If you dont have 1 solid mil to drop, dont think about it. Lets even say, on the simple side, if you dont have 50k to toss in the toilet, dont bother with open-world / multiplayer. Im not kidding. Unless your team can make 100% of its own assets, code, blueprints, network solutions, etc etc, and, is ok taking 0 pay for at least a year … then … then you maybe ok lol.