For someone who is self managing a portfolio of rentals, any recommendation for bookkeeping books?

If so, I would recommend to think not as a homeowner, but rather as an investor. 

If you find someone (or multiple agents) who are taking advantage of similar marketing strategies, you can get more inquiries this way.Lastly, I'd recommend an email campaign to all buyer, listing, and rental agents who are active the same area as the rental listing.All the best!

I highly recommend you travel to the market yourself and spend a couple days driving around, looking at various properties, if you are going to be buying anywhere.  

To put it bluntly....if a company can't take 15-20 minutes and talk with an investor about the market and the possible purchase of a property, they're not a company I would recommend working with.

Highly recommend Nashville. 

@Seth Rose I strongly recommend you find the best cash flowing property possible and buy it with financing out of the gates, rather than go the BRRR route. 1.

Did you work with any real estate professionals (agents, lenders, etc.) that you'd recommend to others?

Highly recommend you start listening to any of the BiggerPockets Podcasts and pick some various topics you may be interested in and see how you may be able to take action, the most important thing you can do!

Unfortunately, I do not have any recommendations but be careful on who you select.