I purchase as primary residence, and then move and rent when I have a new downpayment saved.

While not in TN specifically, I have assisted clients do as you have described: live in a property as a principal residence for 2 years, rent it out for 3 years, then sell.Based on the situation described, you would appear to be eligible for the MFJ joint exclusion on principle residence on your 90% share.However, in order to retain that ability, the house will very likely need to be sold (ie, sale closed, not just under contract) by the end of this month. 

Investment Info:Single-family residence buy & hold investment.

the one you live in would qualify for the primary residence exemption. 

After operating the STR for the first year can we turn the STR into our primary residence for 2 years then sell and avoid capital gains tax and depreciation recapture instead of doing a 1031 exchange?

Investment Info:Single-family residence buy & hold investment in Orlando area.Currently under contract for a single family home that we will be utilizing as a short-term rental.

My wife and I are still in the 'learning phase' as real estate investors, but we know for sure that in the next year (a) we will be converting our primary residence in to a rental, and (b) buying another house that will be our primary residence for 1-2 years so that we can qualify for an owner occupied mortgage.

Today, this is a highly developed residential area close to the downtown of a newish city.I doubt that the current residents know about what is buried on their land.

My husband and I currently reside in Mount Pleasant, South Carolina.  

Since they have been good residents, they can stay as long as they like, but we are not accepting applications for new section 8 residents.