For mmo You should not use any hax, you need proper handling of that stuff or you get in potential trouble later on. (and probably do it in C++, so it is more stable)
I also suggest you focus first on ground level stuff. Doing multiple monitors support is kind of mid to late development.
So first you should find what is needed to make mmo working, like some backend or maybe sdk for mmo.
This is same problem like with making cool and pretty levels before you made any gameplay and movement code (that is trap i fell into multiple times, because it is fun to do)
That time spent on making level is usually wasted because later on you have different speed of movement, height of jump maybe bigger packs of enemies etc.
And you spent weeks doing really nice looking map that does not work with gameplay.
Same with coding any gameplay systems before you have working backend (or at least idea how you do backend)
However if you dont have manpower or $$$ to make mmo yet, i should suggest making coop multiplayer with private servers up to whatever number unreal supports out of the box now.
I really would buy rpg game that have private servers, modding support. So i can invite my friends to paly with me.