Now, I am up for bigger challenge.

Now, in my dotage(I'm 44;) I look at the portfolio and can clearly see that the theoretically lower cap rate properties have been substantial outperformers over the years on the metric of cash flow- so I'm pruning the challenging(and capturing the principal appreciation, *wink wink*) to replace it with the chill. 

Monitors are not bad (propane or ng) but keep in mind ... with any "single source" heating idea, there will be challenges (one room cold, the other too hot, etc.) -- You mentioned propane.

Only challenge is my business hasn’t been established for a full two years yet.

I have a general idea of what I'm looking for, but coming up with a potent goal is challenging for me.

It's been a challenge getting him in on the duplex plan. 

. +1.5% growthAlso, while Phoenix has it's share of subpar construction I don't think it's unique to the city and I'm sure Baltimore has it's newer home construction issues.

We had to do some lender required repairs - finding competent contractors always a challenge, even if your properties are in the same town you are! 

They still require you, the investor, to conduct proper due diligence and to keep your head on in case any challenges arise.

You are in a safer position keeping a security deposit to cover back rent than you are to cover damage in most cases, as tenants can more easily challenge damages.