If you present the listing well, put it on multiple platforms and are asking a reasonable rent you will get plenty of interest and applications quickly. 

My thought is to help him out by going in 50-50 partnership for many reasons: half down payment, half capex expense, strong co-signer on loan, me being local to investment property to take care of little things that need attentions (he will be out of state for his job/I will have PM), etc.  1. 

Any recommendations to get honest and reasonable estimates and get the work done.

For a variety of reasons, including keeping this potential project "need-to-know" only right now, I want to get a ballpark estimate with full understanding that the goal posts could move in either direction as the project gets more discrete. 

Assuming I also use the Airstream for lodging while traveling for personal reasons, would I just take a pro-rated amount of depreciation for the amount of use that is business vs. personal?

Greene Met is very reasonable to work with for the most part. 

We have a reasonably high income from our W-2’s and rents with annual income in the $250k+/year depending on bonuses & OT worked and is usually closer to $300k.

Additionally, any existing restrictions at the town level (there are MANY) will be abolished, unless deemed "reasonable" by the state.

There's usually a good reason why the entry points are lower.

Many inexperienced investors pass on the deal you listed for the reasons you listed.