Dude I don't want to sound pessimistic, but:
-An MMO is not an easy task AT ALL. How much player do you want to sustain?
-Mac support with Construct is not that good. For ios forget about the p2p connection so you will have to have lots of server and this will cost far more than your development cost. Plus it will need LOTS of optimization.
If you know what you are doing then go on. If you never done such a big game before don't even try. It will fail, I tell you from experience. Try something simpler, preferably without multiplayer.
Just a friendly advice.
By the way what is your specialization? Do you program?