You know there is a reason they say most people dont complete their first games - it takes longer than you think, you get bored/tired/stressed, you run out of money, or you think of something new to do. The risk is higher with a bigger project.
I would say absolutely do not touch an MMO style project without a team backing you. At least one or two other experienced developers and some experienced artists, and also all of you should ideally have as much free time as possible. Else dont bother, you will get frustrated and quit long before you have anything playable.
Think of something you can do that will take around 3 months part time, and not be too heavy on the art.
Last year May, I quit my job, and from June I worked full time on my game, which is written in C++ and uses the Ogre rendering engine. As of right now, a demo is still about a month away. That's working full time. Maybe I'm not the fastest coder in the world, or maybe the project I chose was too big. And its single player, not multiplayer. Well I'll add multi player later, just not yet. Its a turn based strategy game. A lot of time was spent implementing terrain, GUI and fog of war stuff, and I'm working on AI scripting right now (using Lua).
Especially if you have a full time job, choose something quicker to do, or get other people on board.
Paul Atreides, Rand al'Thor and Luke Skywalker walk into a bar.
Sh*t gets serious.