How should the mmo server be made? In unity with a simulated world?

I need some advice on how should an MMO server be made.

To be specific, i'm new to this, and i am currently making a little mmo for my friends, and my be more in the far future. My problem is:

Should the server be made in unity? if yes, then how should world simulation work? Is that an option to create the game as the server, load only near-player stuff, and move the characters as input comes from the client on the network?

Sorry for bad english, i hope you know what i wanted to say.

Thanks in advance.