"I do not see the roadmap" I am trying to find this.
But these 2 posts below does a good job summarizing the stages to go through to graduate from area 51 and become an official stack exchange web site.
Notice that this is just for graduation phase from area 51. After becoming an official stackexchange site, there is no more any such requirments on how many questions per day, and any such thing. The site then just runs on its own.
Here is the summary from the above:
There are 3 phases to complete: 1. definitions, 2. Commitment 3. beta. Maple last time went to Commitment phase only and stopped there.
"A proposal needs 60 followers to complete the definition phase."
"200 committers, at least 100 of which have 200+ rep on any other site, and a high enough commitment score"
"Broadly speaking, you will need a community of at least 300-400 avid users (minimum!) "
"The second hurdle is Commitment where you'll need at least 200 users to "commit" to using the site if we create it. 100 of those users will have to earn at least 200 reputation on other Stack Exchange sites to move the proposal on to the Private Beta."
"Finally, if the proposal makes it to Private Beta, you will have about three weeks to attract enough users to curate at least 150 high-quality questions to become a fully listed public site"
So the bottom line, is having lots of users ready to sign up for it. At least 400 or so users (but with half with high reps, 200+) is all what is needed. From the screen shot above by Acer, there was 120 users commited on last attempt. (I do not know if there was more after that screen shot was taken). I also rememebr many did not have high reps (i.e. over 200 rep) so those users did not count, and that was one of the main reason why Maple did not make it.
There is also a time limit to obtain this number. I do not know know the time. May be few months or so. Will try to find out.