What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

In the past I have always done so and I have been discriminated against and not been allowed to rent even with perfect rent history and great credit every single time expect once.

Interest rates, insurance hikes, rise in real estate taxes, eviction delays, rising expenses and delinquency are just a few problems investors are encountering.

Only interested in STR due to tax benefits unfortunately. 

Screening college kids is tricky, they don't have any credit history, and I'm not going to call their RA (if they're straight out of the dorms or their parents house).

Are there any tax implications or mortgage barriers to building a home under the "second home" plan and then converting it to an investment property shortly after its finished?

Underwrite allowances for - Vacancy, Prop Taxes, Insurance, Utilities, Repairs & Maintenance, a Reserve Account, and Property Management. 

And taxes? 

You'll want to make sure you understand the K1/tax filing implications because if you own very small piece of let's say 10 properties in 10 different states you would potentially receive 10 K1s (one for each deal) and 'may' have tax filing requirements in 10 states. 

I'm hoping I can get some tips or pointers from anybody with experience in land development or buying land off tax auctions.