My background in software process improvement if filled with ample case studies to say both are important.  

Is City-Data's high low property evaluating software a good source when you do not want to constantly bother realtor's for comps to determine ARV?

Use Quickbooks or Quicken, or some other accounting software that can present your information professionally. 

Reading about "web scraping software" and all those excel spreadsheets has definitely been fair warning: this is serious business.

I personally will never use turbo tax or any software like that again because at the end of the a really good CPA will be able to help you save money or structure your taxes the way you want them. 

I currently own 10 rental properties and am looking for a property management software that I can grow with. 

Which software have you found the most beneficial?

I'm kind of debt averse, especially since I will already have two mortgages.I am planning to go with a rental management company so I don't have to deal with the hassle of managing it since I am a full-time software engineer.

Not sure about the most practical approach on your side of the line, but when we started our real estate {ad}venture, we took a chunk of retained earnings from our software company and funded a separate entity for real estate.   

LOL  It has also lead to me learning the pure shear value of open source, especially when it comes to landlord software.