As somebody who is kicking themselves that they didn't get in on this interest check and discussion earlier, here are my answers to the questions.

[indent][b]1). Multiverse or Single Universe?[/b][/indent]
My heart says "single universe", but because I'd have worries about trying to fit everything together in a way that makes sense, my brain says "multiverse". Perhaps some sort of compromise could be reached involving sticking thematically similar cartoons into their own universes - it'd require a bit of work to make these groupings, but having three or four "canon" universes might be better than everything existing in their own.

[indent][b]2). Sandbox or no?[/b][/indent]
Much like my answer to number one - [i]why not both?[/i] I prefer games where there's a bit of structure, to keep things moving along. I'm not so cynical to say that people [i]need[/i] a GM to tell them what to do, I'm sure people can come up with their own plots, but especially at the beginning of a game, a bit of gentle herding to get people moving isn't a bad thing. There's almost certainly an interesting discussion to be had about why sandbox games don't work so well to be had here! Anyway, a game in which there are "here are things to do" with the occasional bit of "sandbox time" would be my preferred choice. 

[indent][b]3). OCs?[/b][/indent]
I'm happy with OCs, though I probably wouldn't play one. If the rule was "No OCs allowed!", it wouldn't be a deal-breaker for me.

[indent][b]4). What qualifies as a Cartoon Network show?[/b][/indent]
The stuff that people have listed already is a good start. If it were me running this, and it's not, and thank goodness for that as I can barely keep my [i]own[/i] game from turning me into a gibbering wreck, I'd start the list with "[i]whatever people want to play a character from[/i]" and go from there - if somebody desperately wants to play a character from a 1970s cartoon that was re-run on Cartoon Network, then it's in the list.

[indent][b]5). How will comedic characters fit?[/b][/indent]
Go Punch Time Explosion and make everyone a fighter if it's going to be an action focused game. I like comedic characters, and I'm weirdly happy playing somebody who is absolutely useless in a fight, but if the main thrust of the game is going to be "action", not being able to take part in the action stuff might mean not doing much of anything, which would be dull, and make me sad.

[indent][b]6). Anything else?[/b][/indent]
Could I reserve [i]BMO[/i] from Adventure Time?