Does anyone have any info they can share about investing in properties that have had unpaid taxes for a long time but aren't on the sheriff's auction or resale list?

Principal Paydown- If your loan term is say 20 years. 

Some investors also use a business line of credit backed by their cash flow, which can help with future deals.If you’re planning to scale, maybe start stacking that cash for the next property or even park some in T-bills for short-term returns.

Use terms like “urgent habitability issue” and “potential legal exposure.”Send a formal demand letter via certified mail, informing them of a deadline (like 48–72 hours) to respond.If they continue to stall, file a complaint with your state’s Department of Insurance.

@Steve Chaparro How long before ATM's are completely obsolete?

The technical term is Sound Transmission Class. 

What if they change the terms on you last minute?

I had a duplex in FW long enough for it to be mortgage free. 

To make a long story short, I have always been interested in real estate, but I'm very unsure as to where to start.

Thats fine as long as your Debt to Income (DTI) supports it.