You bring up a lot of good questions and hopefully I can address them all.The seller is a gentleman in his 60's whom owns this lot in a trust with his wife.

Previously I managed quite a bit of REO rehabs in the Atlanta area as well when I was a construction manager.

I’m going to check it out tomorrow with my agent and also trying to get our GC in there with us for an estimate of rehab.

Call a few local property managers and tell them the address and see if they can offer a rental estimate based on comps.

Being in California, I have to send a list of charges within 2 weeks, but she left no forwarding address.  

When we were buying to live in the place before becoming an "investor" we were waiving the contingencies to compete with the all cash offers in the Seattle area.Bigger Pockets also has a book called Estimating Rehab Costs.

Could I just hire a crew of guys (experienced and insured obviously) to do the rehab without the GC? 

Since I am working every day to find new leads it's not possible for me to check upfront to see if I have a good probability of hitting the right address based on public data on the first mailing When I get the returned postcard I utilize different methods to see where did the owner go.

        Purchased this one for $89k with a $60k Rehab $249k ARV and as with most rehabs it's taking longer and costing more...Besides that due to Hurricane Harvey and an already tight sub-market I am happy to say it looks like our ARV may be inching up over the next month or so which is GRRRREAT!

The CMA of the property would be around 430k-450k looking at recently flips homes close to the property (not counting the extra 400 sq). we talked to other investors and came with a rehab cost of 50k give or take, again this is our first work so we might be off by more than we would like to. the Owner of the house seems more than willing than to finance the project 100% by either using his business credit or even taking a HELOC on the property we are flipping.