Wow. That sounds daunting. I'd like to see how you make that work!
Surprisingly, the core setup doesn't seem too bad so far. Practically speaking, the code needed would be:
Some sort of level ASM to add a counter to the status bar for mini games
As well as a similar counter for lives (since it shouldn't kill Mario if he runs out, just send him back)
A check to see if 10 have been completed that redirects to the next area with the Dragon coin
Maybe a random number generator to work out which of however many microgames are going to be loaded
Along with code to redirect to them
Special level ASM for each microgame which acts as a timer, teleports Mario when timer runs out and removes one life, adds point to score if he succeeds, etc
The complexity comes less in each part (which practically speaking, is probably not that much code) but having it work together flawlessly.
Oh, and I need the graphics too, since no one's ripped the elevator BGs from the WarioWare series for some reason.