On a low end that would put me at $1500 left over after all expenses.Notably, my long-term goal is to continue buying 3-4 unit multi’s and these retirement style commercial buildings.

She just sold that to move closer to us and as house prices are a lot lower where we are, she had quite a bit left over. 

If you think about it, I would pay practically a down payment to my landlord in 3 years. (40 months x $1500 - $2000 = $60,000 - $80,000 of rent) Instead, I will put every penny leftover into my mortgage and pay below the 80% threshold, likely in 2 years, to get PMI removed.

Hopefully you have left over paint and that is an easy thing, I wouldn't necessarily charge them for unless there are large holes in the wall. 

We would sell the home between $250-300k, and we would buy land between $150-200k so there would be cash left over to use. 

A fourplex might be around $250K, where even if you put little down and you pay the difference, you still have cash left over to buy more rental properties.

I can qualify for a conventional loan at 20% down but I wouldn’t have quite enough left over for the $20k reno costs.

You will probably find there will be little cash leftover if you hire this out so I'd encourage you to try to manage it yourself to begin with then if it's not sustainable for you, try to find someone to take it on.

Assuming that minimum, I would only be spending about $250 a month on average, which comes out to $3,000 a year, with $27,000 left over (or 25,500 after taxes, assuming I contribute about $5,000 to an IRA that year, which I full intend on doing) for the above. 

Some leases use slightly different language saying these items are "payable BEFORE rent" meaning that whatever money you receive pays those items FIRST leaving unpaid rent leftover.