Then we setup these ozone machines and let them run for a few days all over the house.

First of all, their certification program is NOT accredited by any legal body so it is basically worthless other than it may look good on your wall.

So I understand the owner loses right to possession once some body buys the tax certificate?

It sounds like you are looking for an employee as defined by most taxing bodies.

I tried calling around the respective govt bodies, but wasn’t able to get clarity on whether out-of-state investors can setup such a facility.

You'll need to provide Entity Docs for each LLC that is a part of the transaction so that the underwriters can review them all the way down to the natural individuals/warm bodies. 

You need to contact the governing body that has jurisdiction over the zoning laws for either the incorporated or unincorporated of the county or city for the plot you are interested in building on.  

Response to #1: Some lenders allow for layered entities while others want warm bodies/natural persons to be direct managers.

i bought property at tax sale auction in Dekalb county Georgia, over 12 months ago, now i am doing barment,  i published ad news paper,  i sent 30 days notices to ex owners and all parties might have interest,  and the property now it empty / unoccupied.my question is: if 30 days notice expired and no body redeemed, can i enter the property and start to fix / repair the property, and rent it??

A good clean and a few hours of ozone and its totally gone.Would I rent to someone who was super stoked on 420?