See what rents are in the area for comparable properties...rentometer.com, mapliv.com, hotpads, whatever you wanna use.

I didn't realize it at the time but now that I'm comparing 6a to 7, I think my edits to 6a(changed full months rent to half) are now going to conflict with #7.

Owner financing is not anymore dangerous compared to other conventional lending options available.  

CAP rates are generally used only for commercial properties, so you can compare different returns based on two completely different types of commercial properties.  

I found several online but I don't know how to compare them.

Ask the agent for comparable properties.Just a few ideas to consider.

and comparing it to NOI... eeeehhhh I'm pretty sure that you're $275k more in debt than you otherwise would be, so you need to factor that in.

Is it as easy as estimating ARV through comparable sales, or should I downward revise ARV ~10% to be conservative?

the bright side of finding BP after you've already had a deal is that you can focus and have a frame if reference for the info you get, compared to your previous experiences.

Two of our contractors spring to mind, the plumber who despite all the best connections in the world hates the business of rental property, and our tree guy who plays the same game as us (buy and hold) and we often compare notes.Some people like the game, some don't.And again, the debt thing is down to personal choice, although interestingly a friend who spent $65k on a truck has since told us that it's the last time he's buying such an expensive item, and when it's paid off, it's paid off.