The interest rates were lower compared to what they are today.

Tell them you will research comparable and give them a price within two days.

1. walk through inspection with them present to compare to move-in inspection and noticr of non-complaint behavior if any .

Then, you can ask the realtor to look at comparable properties in the area to get the ARV or "after repair value" of the home.  

Instead of being valued compared to comps you be valued on NOI/CaP rate for the area.

What are the pros and cons of such deal versus a comparably sized and located investment in a classic multi family (...where you own the building and land directly).Any resources you guys have that I can educate myself on?

You can check Trulia, Zillow, Rentler and other sites to compare your house with rental homes in the area.  

From a psychological standpoint, I think it's easier to take a little increase every year compared to staying flat for a long time and then a big jump to try to catch back up to market, even if you end up paying less overall with the second option. 

I heard GRM is good metric to use and comparing sales to other duplexes that sold in that area.

I'm interested in hearing from experienced investors who are in position to compare different methods of passive investing.