Can't say what's hardest, too many moving parts but take care of your tenants and build that goodwill, pays off in spades.

Most sellers only care if you close so you can usually use another form of capital stack other than what is on the agreement, however, the seller can force you to use the originally agreed-upon payment method. 

My assumption is that there are a lot of bad apples, and very few that actually care about the seller.

The code being cited by the inspector is below if you care to bother.Thank you.https://codes.iccsafe.org/content/IPC2021P3/chapter-7-sanitary-drainage#IPC2021P3_Ch07_Sec708 Could you put cleanouts within the interior (is there a basement?)

Staff often seemed to focus on one requirement at a time, and only moving on to others as each was taken care of, instead of starting them all at the same time.

Highlight features and amenities they care about most.

This is one of the things that @Matthew Irish-Jones mentioned above - be careful about putting #3 on his list above #1 and #2.

Unfortunately, every state and every locality has different laws and what works in one location doesn't always work in others, so you have to be very careful about the 'free' advice that is given in online forums. 

The GC is a business person who doesn't care about your ARV, LTV, or your budget.

Hope this helps for now, and great to hear you are paying attention to your hard earned retirement funds with such care and discipline!