A good site to use if you want to do your own is redfin.com When you run a search, filter the criteria and on the right side of the page it will list all the properties that match that, at the bottom of that list is an option to "download all" and you can export the file to a excel document and run a comp analysis

What sort of qualities  should I look for in them to know they would be a good match for my investing career?

All tenants' deposits have been taken as well.  

I'm not sure if I should ask for a non refundable deposit or just wait until I assign the contract to them.

Sounds like a wholesaler if they want a deposit upfront.Question #1- Are you a wholesaler?

Her behavior made us decide to offer her the entire security deposit back if she and her family would vacate the premises by the weekend and find a house that suited them better.

He did not respond on his possessions, but asked when he would be getting his deposit back?

  :)And there are companies here in Oregon and Wa that hook up with RE brokers , ( these companies are HML) they track all the sales have a very sophisticated software system. they bid for you and also provide the cash for you at sale.So it goes like this.say you want to bid on a 200k house you need 40k. you deposit that with them.they win the bid they put up the 200k .. they take a security interest on the recipt from auction.. then when trustee's deed comes they roll that into a HML.they charge a fee for the buy .. and then charge you for the HML usually 4 and 14 , and then you do the rehab and your free to use anyone to resell. 

When we run the credit report, it will show previous addresses and alias names; the addresses will either match up or they won't.

Should I collect a security deposit, and upfront payment even though I'm sure he did that with the previous landlord?