Due Diligence; Where do I start ?

[John McAffee]

Hello all, For the past couple of years I've told everybody and their grandmother "I'm thinking about getting into REI" with out really going anywhere. The last few months, I've been listening, hardcore, to the BP podcasts; I've bought and read a lot of the books the guests have stated to be their favorites (the Amazon delivery person probably knows my address by heart). The one thing that most, if not all guests have said, if not all, is "You've got tp do the First Deal".

I'm trying to push myself past the Analysis Paralysis portion of REI. I've recently found what I believe to be a "deal" on the MLS (Realtor.com). The only thing that makes me fearful, it has been on market for like 130 days.

It's a separated duplex that needs... everything. Obviously, many have looked at it and decided to run the other way. I keep looking at it and trying to calculate costs for repair, etc. 

My question, How do I go about looking up "Comps" and any other thing I have no clue to look up? Any and all advice is welcomed and wanted. I'd like to look for private lending, but I know that I actually need to have a deal to present. Where do I look to do this "Due Diligence"?.