You can rent the floor sander from HD if you want to diy. just make sure you read up and watch videos.

Where this gets weird is the job codes I used to put in on my HD Pro Xtra account.you had to get the name down to three letters or numbers.

Your first 2 flips you called HD & Lowes for cabinetry & flooring.

I have looked at the Thoroughbred II at HD ($0.88/sf), but do not want to install and it ends up looking TOO cheap / terrible.I am thinking along the lines of new-build apartments / builder grade equivalent carpet?

I am surprised they are running out of hot water fast, the smaller tanks should heat the water faster than the larger 50 gallon tanks, maybe look into small tank heaters with more heating coils to heat the water even faster. take a look at this one, available from HD too https://www.rheem.com/product/marathon-30-gallon-e...that one may deliver enough hot water for your tenants.

You use credit cards from Lowes or HD.  

The prior tenant had contacted the HD without even notifying the property management company until we began getting notices.

New carpet was installed through HD and was put in for under $500.

I buy mine from Lowes or HD.  

IMO, not worth dealing with used appliances - all savings will go out the window with the first repair call. unless of course your lease agreements explicitly require tenant to maintain appliances (not typical in CA but common in mid-West)Personally, I always buy new from HD and always get 5 year pro warranty - covers all repairs and in a few cases ended up with new units when they could not fix old ones.