Start checking Zillow, Redfin, etc., for both rentals and sales prices. 

a lot... a ton.... off the charts.... not even close...Check real comps in area

A contractor can help yes when it comes to looking at it and telling you how much or what you be looking at if you want to upgrade or fix something visible but you need the inspector to check out the roof AC and plumbing thoroughly despite what it looks like in person I’ve seen mini jacked up ceilings.

I'm a licensed realtor so I have access to the local LMS, I check out public LMS sites, Facebook, Craigslist, and the few deals I find are gone far too quickly...I work a full time job and do real estate on the side.

If you go the new home route, check the rules on resale and if there is a right for the builder to purchase it from you or a minimum time before you can sell it. 

If Airbnb has confirmed these are Service Animals I wouldn't make any waves and see if there are any issues after they check out. 

check your local laws as a few people on BP have posted that you can only do evictions for unpaid rent in some areas.

Yeah that map is a great starting point and something to double check areas with if new to the area...we work a little more on a street by street, neighborhood basis, so it's gets a little more specific. 

I also open up Airbnb and/or VRBO so that I can cross-check the properties. 

I am not saying you have to hold your money in a checking account, but some savings accounts are now earning 2%, a 3 month TBill is over 4%.