Yeah.
About the map, however, you don't "pick levels". It will mostly be there for reference, and to show you ways to get to place Y from place X. It will just look like SMW, not work like it.
Also, I'd like to add to the narration thing when it comes to battles... you can just say your action, but it would be cool if you narrated that as well. For example, instead of saying "I use Punch", you can say "Nan ran up to the enemy and threw a fist in his foe's direction", or whatever. If you think your narration doesn't make too clear what you're doing, you can just add between brackets what's happening.
"THAT'S IT, YOU MONSTER! TAKE THIS! HAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" he yelled before blasting Nan.
[Megaboy X uses Buster.]
I'll also use the brackets to comment on the technical details of the battle, and clarify the effects of the attacks and whatnot. (For this example, Nan is controlled by the gamemaster)
However, Nan saw that coming and he quickly leaped out of the way.
[Nan's Pretty Lucky badge allowed him to avoid all damage this time.]
"You'll need to do more than that if you want to defeat me!", said Nan. "Here I come!". Nan then rushed towards Megaboy, who couldn't stop him from punching his stomach. Nan then quickly threw a hook to his face, then another, and then threw a roundhouse kick to his side. Megaboy looked a bit hurt.
"You're so weak", said Nan.
[Nan used Combo, managing to get critical thrice, allowing him to strike four times, dealing four damage to Megaboy X. Mega's current HP: 3]
Yeah, poor Mega.

But yeah, there you have an idea of how it might work.
Edit: Six players so far! This looks like it's gonna be awesome.

I'll try to get this show on the road by Monday. I just gotta take some time to... write the plot down... or something.
Also, could someone take the Yell or Intimidate skills? I made those so someone would use them... they do get quite useful later on, with badges and stuff...