You have no clue what you are getting yourself into.
As far as i know there is no such thing as a "(M)MORPG Do-It-Yourself-Development Kit for Dummies". Multiplayer Games are hard work. Multiplayer realtime 3D games are even harder.
Further you arent really specific in your needs at all. The needs of a Shooter might differ greatly from those of a ... say RTS. Thus the engines would differ greatly in terms of rendering mechanics, networking etc.
I am with no means an expert on this topic though and i might underestimate your expertise greatly by packing you with the cliche "I want to write an awsome multiplayer game after i mastered HTML now!" guy... I Also dont mean to discourage you in anyway. Its just... if it fails - which has a great chance to be the cas specially in a 5 year project - you possibly wasted a lot of time for nothing.
Of course: You can learn a lot in the process if you do it right. But if learning isnt the goal than it is better achieved by smaller projects where failure isnt such a great trigger for frustration.