The PP doesn't require any software. You're computer will (should) see it as a flash drive right out of the box. It comes with all of the accessories you'll need to get started.
The Calibre program offers free news downloads from a bunch of different sites formatted as ebooks. Calibre is a free program that also does a nice job managing and converting ebooks.
No problem at all supporting two books. Your computer won't care and Calibre only knows what's currently connected to it.
The PocketPro can read DRMed books in ePub or Adobe format
EXCEPT from Barnes & Noble. Lots of websites sell books that it can read, including Sony, and your local library may offer ebooks it can read.
I'd invite you to come visit the Astak forum (
https://www.mobileread.com/forums/forumdisplay.php?f=204) to get questions answered by the larger community. Calibre also has a forum here where the developers offer lots of support.