Moved back to Maine almost 5 years ago and have scaled up quite a bit to my current 45 units in L/A.

This team will help you scale your assets accordingly so they continue to grow and improve your net worth quicker than current. 

https://www.biggerpockets.com/forums/52/topics/82174-ultimate-guide-to-tenant-screening-and-renting-your-houseEdit:  Unless you are referring to more property management on a larger scale. 

@Nick TalaricoAs suggested - it helps to have a separate bank account for just your real estate related activities.This way you know 100% of the activities within the account are related to the real estate related activities.You can export the information into excel and properly categorize the information.One you scale up, you may want to consider having an accounting software such as quickbooks, Stessa, Quicken, etc.

It typically takes scale to achieve this.

Small multi-family is good With goal of getting to larger size as quickly as possible as scale will help make life easier (think self-managing vs property manager managing).  

Also Nashville has a diversified job sector as well (tech, auto, tourism, logistics, healthcare, entertainment, manufacturing, etc.) 

If where I live had cheap houses in the 50k range then it would be a no brainer for me, but I live in CA where scaling wide to start is impossible because properties are so expense (1-2% rule aint happening here) so I have to make some hard decisions about what my goals are for getting started.I wish there were some general guidelines that work for all newcomers, such as invest local with a single family home and learn about fixing it up and being a property manager (conservative approach), which seems to be the only choice for some people.

The problem I keep running into is scaling.

It is a learning curve but if you are a fast learner, coachable and can lead and delegate a team it can grow and scale fast.