But maybe that's just me...In your case, it sounds like they have buyer's remorse and are ashamed to tell you after signing, but also don't be surprised if they show up on the 31st. 

About a year or two ago I pivoted and started flipping and finding alternative strategies, but I have realized those cannot replace this strategy, they can be in addition to it, but I need to continue buying, moving, and keeping as a rental every couple of years because this really is the best strategy for building long term wealth.Did you work with any real estate professionals (agents, lenders, etc.) that you'd recommend to others?

Going lead free in old homes that are pretty 1950 usually means eliminating old radiators, getting the lead off them, or replacing them as well as eliminating all old trim aa well as cornices and even fire escapes. 

Sounds like a good place to start (for both of us).  

The concern arises when you're acting as an agent for others—there, the law is stricter.Since you plan to use the agreement for future properties too, it might be worth getting legal guidance upfront, even though the $1000 fee sounds steep.

When I used vinyl surrounds, yes it was much cheaper, but I had to replace almost every turn over.  

Durable and easy to replace if one gets scratched.

Being a tax professional I would say currently it doesn't sound like something you need just yet.

The potential issue is that he may have gotten his interest rate when rates were lower and you may get the deal at a higher interest rate which can potentially have the deal at break even or at a loss.The quality of the deal will depend on what your net income is and what you are putting into the deal.If in the above example and you have the same net income, the deal sounds amazing if you are putting in $200,000 because you have a 10%+ rate of return.But if you are putting in $2,000,000 the deal is horrible because you are making 1%

It sounds like you have a solid strategy in place for scaling up your portfolio quickly with seller financing and focusing on properties that cash flow immediately.