I'm getting a contractor/ structural engineer to come by and help me draw estimates and understand how serious these issues are.

Reno and house appreciated quite significantly 400k to 550k estimated. 

Just go through them, select the renovated/closely matching ones, and enter them into a model.Here's my fix & flip model, you can see the comps entered and some quick stats below them: Then I use that comp data to adjust the Sale Price in the model to what I estimate it will be (double check the resale $/sf is in-line with the comps), then adjust the purchase price until I hit my desired return level. 

In 8 years and over 20k reservations we have had 15-20 incidents I would estimate. 

We estimated the ARV to be $150-160k.

Neither outcome is good for you.I give some approximations of each expense category in The Hands-Off Investor, but the best way to nail down operating costs is to look at the property's historical performance.For example, Contract Services and Utilities. 

Estimated about $25,000 including utility hookups.  

I only have 1 month of proof of concept so I need at minimum 3 months to get a better estimation. 

If you can get a loan at the 6.5%, you're saving another 5k a year off your estimates. 

It’s a good move to have a contractor walk through before making an offer to estimate costs and timeline.