Average/median rents seem to vary depending on which site I look at, lol - perhaps you know reliable sites to use for this? 

In CO, I am close to many military bases and have posted on their sites but wasn't as successful as just listing on airbnb and Zillow.Best of luck,Lindsey

I read on here that it is a waste of time and money to pay any site for help and there is plenty of free info on the web.When I try to google for this free info or lists all I get is sponsored sites trying to sell their programs.

You can do this research on the OTA sites, AirDNA, Pricelabs, and other similar sites. 

The site has tons of resources, almost too many!

You can literally find answers to all of your questions within the confines of this site.

Go to Etsy and search for "rental property tracker," and you will find hundreds of nice spreadsheets to track 10-20 rentals, usually for under $10.Software has extremely helpful features like online payments, marketing syndication (click a button, and your property is advertised on multiple sites), electronic document review/signing, maintenance tracking, and owner reports.

And the need for you to reside on site in order for the business to work. 

Many people on this site only are interested in a specific geography.What type of product are you looking for? 

Some areas are strong on both sites but does seem to lean one way or the other.