Taxes are also always going to be a consideration, and this is an assessment year, so you should account for them going up more than usual in your projections.  

The property is being sold as raw land below its tax-assessed value.

Oklahoma may require you to file a state tax return regardless of your income level.

There was a property at the auction that sold at market, however it had a federal tax lien of over 100k attached to it.

I pulled them from the tax assessor's website, just going one by one through each parcel to locate and identify the vacant lots.

Typically, it just refers to the number of units/leases you have, not the number of tax parcels. 

There has been no tax benefits per se.  

If you are setting aside funds for capex, taxes, insurance, or other expenses that don't occur monthly, transfer those funds to Savings each month and hold them there until it's time to spend them.

Ignore the loan when trying to factor in the possible tax implications as paying off a principal balance doesn't do anything tax-wise.

Given that you've owned them for almost 5 years, there is also a good opportunity to do a cash out refinance and obtain tax free money that you can use to expand your portfolio even further.