Most of us who grew up as developers eventually, recall that time, of making another biggest MMO ever.
Regardless of how much I would love to make my own MMO, with experience I’ve got for coding 10+ years, I will clearly tell you: making MMO - is hell of a job for teams of 10s or 100s people.
Even only few top-class indie teams capable of making something at least a little bit MMO-ish.
The best advice:
Start small, build small games, learn small bits, technology, maths, and all other little things. When you put your knowledge together then, you wont be asking questions of “how to start”, you will know the path, but it wont be easy one anyway.
Make a little cool games, publish them, engage with community and once you get ready after few years, consider starting something little but already MMO-ish.