A normal 2 x 4 wall takes R13, which means you want to add another 5 to get to R19, you can achieve that by adding 1" foam on the outside ( R 5.6). you should break down your costs and find out what is best for you: add 2" framing and 2" extension jambs to windows( material and labor) + R19 -- leave existing 2x4 and spray foam-- install 1" foam on exterior,R13 interior, extend jambs and trim on exterior ( if vinyl siding that can easily be covered with aluminum). 

I would happy to pay a few bucks to chat with someone who has extensive experience selling performing notes as I have originated a few, but never sold any. 

I purchased a 4-plex back in June with an FHA loan and the intent of occupying a unit. upon taking ownership, the unit I was planning to occupy needed extensive cleanup, and I have not been painting and preparing to put in new flooring.

What's your relationship with vendors to conduct turnovers quickly and reduce vacancy?

First if the deal is really good for you I would sign a deal with contingency to close in January 2021, reason for the federal government eviction moratorium will expire 12/31/2020 but that’s not saying they will issue an extension.

I was thinking of wording it as something like"Inspections will be conducted as necessary"  or"Mandatory inspections will be conducted every six (6) months.

We invested approximately $40K into the rehab of this property and rebuilt the back deck, repainted the exterior, conducted siding repair, installed new flooring, repainted the entire interior, and updated the kitchen and bathrooms.

The two primary are to move family into the unit or to do a rehab extensive enough that tenant cannot occupy the unit through the rehab.  

I make the place nice and I do go near top of market rents… but, I also try to incentivize said people that if they will consider a lease extension, I will provide a small discount on rent and not raise rent. 

Now that you have a history of conducting these sorts of deals it may be easier for you to convince lenders to do business with you.