Whats the benefit of preorder and other Q

Usually preorder is cheaper but if Im not wrong its same price in this case? I can play beta I guess but its ending in few days.

Do I need to create MS Live account for this?

Can I choose ingame nick or will it use my Live/xbox name?

Will Steam and other versions share multiplayer? Or if I buy now I wont be able to play with Steam players?

Im a huge AoE fan, even p(l)ayed AoE online. But thats the thing, I dont want to waste money. AoE Online had potential but they did everything so badly it was unbelievable. I want to be sure AoE DE is worth it. Right now Im a bit worried about the popularity.