@ejaigner

The prevaling rhetoric on the net is one LLC per property, which per the IRS means one accounting file for each, so yes in QBO that is one subscription per company.  You can get by with essentials if it is one property per llc.

desktop is one purchase price and as many companies as you wish (as your hard drive will hold).

He needs to consult with a couple of business lawyers as to whether or not multiple llc's is the way to go.

If all the rentals are kept in one company, then QBO Plus is needed, only one subscription though.

a single subscription to QBO is 3-4 times as expensive as desktop over the 3 year support life of desktop, see this comparison, the cost is toward the bottom of the article.  a non partisan comparison of QBO vs QB desktop
http://onsale-apparel.com/Rustler/qbo-or-qbdt