The site proposal is still on Area51, but I'm not sure how to reach it by navigation (I just took it out of my Fullfilled Commitments list). However, as you can see it only shows the stats at the point of graduation, they're not updated anymore (which on the other hand means I can safely quote them here):
At the end of beta, this site had...
10.9 questions per day
Excellent – 10 questions per day on average is a healthy beta, 5 questions or fewer per day needs some work. A healthy site generates lots of good content to make sure users keep coming back.
Excellent – 90% answered is a healthy beta, 80% answered needs some work. In the beta it's especially important that when new visitors ask questions they usually get a good answer.
602 avid users / 11,479 total users
Excellent – Every site needs a solid group of core users to assist in moderating the site. We recommend:
150 users with 200+ rep (currently 602 users with 200+ rep)
10 users with 2,000+ rep (currently 74 users with 2,000+ rep)
5 users with 3,000+ rep (currently 51 users with 3,000+ rep)
1.7 answer ratio
Okay – 2.5 answers per question is good, only 1 answer per question needs some work. On a healthy site, questions receive multiple answers and the best answer is voted to the top.
Excellent – 1,500 visits per day is good, 500 visits per day needs some work. A great site benefits people outside the community. Eventually, 90% of a site's traffic should come from search engines.
Other than that, you don't get much farther than the stats you already found, I think. However, they incorporate many things from the Area51 stats already.