You need to be sure you have a trustworthy mechanic that does not just replace systems at a drop of a hat, as you can replace every part of the system.

Finding a trustworthy contractor whose bid will end up lower or at the initial conservative bid is a big part of your success. 

Both people are highly, highly trust worthy and honest people. 

I haven't been employed in the industry but always being around my brother and friends, I have quite a few trustworthy contacts.I am going to follow the link and start reading.

They have to be insured, trustworthy, etc.

I would recommend having someone trustworthy in the area that can physically go by the each property, take current pictures of the property AND neighborhood. 

If you have located a trustworthy PM company in the area, however, then by all means consider the multifamily approach.

I would say if you already have some trustworthy local connections like local TK provider,Realtor,wholesaler etc, start from there. 

I'd consider your immediate surrounding area within say an hour or less to start off until you build a trustworthy network team to assist with the managing of your property as you look further away from home.

Even more important than the market selection, you need to identify a really reputable and trustworthy team/company to work with.