Just bought 30 huffys cranbrooks for a bike rental business. WHAT PROBLEMS SHOULD I BE PREPARING FOR Be nice. I know these things are cheap. Just wanna be semi prepared.
Forty years ago Huffy bikes were actually pretty well made, just heavy, ugly, and not very nimble.  But now that everything is made in China, as cheaply as possible, it's hard to predict the quality.

First off, you need to keep the tires properly inflated.  This is a seemingly trivial but incredibly important (and often overlooked) maintenance item.

Also set up a schedule to check every bike for such items as bearing play (both hubs, crank, and headset) and chain slack at regular intervals.  And squirt a bit of oil on the chains at regular intervals.

Otherwise, wait to see what breaks.  A lot will depend on how your customers treat the bikes.  Be prepared for some bikes to be destroyed, and for others to disintegrate on their own.  Expect to use damaged bikes as "organ donors" for repair parts for more serviceable bikes.

The Park Tools website and Sheldon Brown's site are your friends.

(I do wonder what provision you have for adjusting seat height.  You may need to invest in quick release adjusters for the seats.)