I have some capital, and a lot of motivation to grow my company.

If those markets are growing population growth is coming!

She noticed something growing on her window and that's when she reported it to her landlord.

I going to try for a larger unit count 20+ and at lease a C+ that is growing or have more potential so there's more up side. 

I’m close enough to retirement age that I could make this my primary occupation within a few years and, with a little luck, invest on my own - but I like the idea of also investing other people’s money as a way to help grow their capital alongside my own.I’m fairly early on in my research but I am stuck on what seems a straight-forward tax problem.

Diversify - Grow your portfolio selling with the 1031 and buying multiple replacements and by doing it that way tap into 100% of your equity instead of the limits in a refi. 

It might benefit you to engage someone that understands real estate investing to be able to take advantage of these discounts, as well as use them to double check your work until to you grow to a point where it makes sense to outsource.

I tell them the basic rules are not to damage the place, pay rent on time, and don't become a demanding tenant with frivolous requests because I will invite them to move to a place they would be happier in a heartbeat.

Post the notice and begin eviction asap or you will be looking over your shoulder for the next 12 months waiting for them to demand their expensive stuff back.

Hopefully they're earnest money was a realistic enough amount that if these demands are not part of the contract and they decide to cancel/break the contract you will get something reasonable.