Moz's Domain Authority is a highly inaccurate metric. I wouldn't worry too much about it.

It is okay for using as part of a filter for ruling out some domains as candidates. For anything else, you can pretty much ignore it.

If you buy a PR2, you should see a PA or DA around 20, also, make sure it's indexed in Google before you buy a pbn.

(SITE I'M LINKING TO) MONEY SITE - DA 36 - PA 32
PBN A - DA 46 - PA 40 PR 2
PBN B - DA 39 - PA 36 PR 3

NOT THE BEST IDEA IF, LIKE YOU MENTIONED:
PBN C - DA 12 PA 10 PR0
I would still like to point out that PBN C still passes link juice, however, unless you got this domain for $10 I wouldn't bid on it. I only focus on above 25 DA and PR 1 or higher.

no, it's better to have backlinks from a wide variety of domains.

Not by any means. If you are lucky enough to have a money site with good metrics, there is no reason why you can't point links from domains with lower DA at it.

Plus, when you point plenty of PBN links at a money site, it will almost inevitably get a higher DA than the linking domains simply by the process of building those links in the first place.