The owner lives out of state and contacted me off of one of my yellow letter campaigns.

Our Marketing consists of pre foreclosure direct mailers, door hangers, networking events, craig's list ads, and email campaigns. 

We have two properties that we came across through our DM campaign.  

you want something like a covenant. they are restrictions put on a property by a seller. your attorney should be able to guide you.

Is there anything being left behind that is considered dangerous and/or restricted to specialized and/or expensive disposal?

I purchased a list of absentee owners from my county property appraiser for a direct mail campaign.

Maybe set up a yellow letter campaign with an investor where you split the leads depending on what the seller really needs.

I don't even use Quicken because it's too restrictive and has a lot of stuff I don't want or need.The best way I've found to build a useful spreadsheet is to just start throwing things on the page.  

If not, and you´re strictly looking for an investment, you´re almost definitely going to be disappointed (that is, unless you develop a portfolio of several STRs in the same location and reap the benefits of shared operational costs). 

San Francisco is out, LA is out, Santa Monica is out, Santa Barbara is out, places in Oregon, Autin, Tx is in the news contemplating restrictions on short term rentals, Ocean City, Maryland, NYC, etc etc etc.