Ah, this is definitely a more nuanced answer than just X links = Y DA/PA... The TL;DR is take a look at sites similar to yours in the Comparison Tool to get an idea around goal numbers. https://moz.com/researchtools/ose/comparisons
Rand has presented on this in the past, and here's one of his answers from the blog that should give you a good idea of what's taken into account...
Q: Can you speak in more detail about the specific metrics that are being used to calculate the domain/page authority?
You talked briefly about this in video 2, and it makes sense that you're using already existing metrics like mozRank, mozTrust, number of links and number of linking domains. But what are the other metrics you use (those "dozens or hundreds" of link metrics)?
Rand: Just a start, but things like:
- mozRank
- mozTrust
- Domain mozRank
- Domain mozTrust
- # of links
- # of linking root domains
- % of followed links
- % of image links
- % of links from same IP c-block
- % oflinks from noscript links
- distribution of % of links from pages with certain # of links on the page
- distribution of TLDs in links
- distribution of TLDs in linking root domains
- mozRank passed through links from certain TLDs
- distribution of mozRank passed through links with certain mozTrust metrics
- mozRank passed by sites with certain DmR/DmT scores
- mozRank passed through image links
- mozTrust passed (on all of the above sets)
- relationship between each metric with each other metric
- derivatives calculated between multiple metrics (3-way, 4-way, 5-way, etc. comparisons)
I suspect there's a lot more in our formulas at this point, but you can basically think of it as us using every metric we can calculate and every metric that can be calculated off the relationship between 2, 3, 4+ metrics.As we noted in the video, the algorithms themselves are pretty hard to look at and find value from, but the concept behind it - that by mashing up metrics in ways that correlate with search rankings using machine learning you can get high value data - is what's important. Hope that helps!
From: http://moz.com/blog/whiteboard-friday-domain-authority-page-authority-metrics
The moz video on DA: http://moz.com/learn/seo/domain-authority