BUT..I am wondering what constitutes a primary residence?

It's in the TX constitution.

*This post does not constitute legal advice and is not to be relied upon. 

It’s in the Texas constitution.

The Secretary shall prescribe regulations with respect to the circumstances under which use of the unit for repairs and annual maintenance will not constitute personal use under this paragraph, except that if the taxpayer is engaged in repair and maintenance on a substantially full time basis for any day, such authority shall not allow the Secretary to treat a dwelling unit as being used for personal use by the taxpayer on such day merely because other individuals who are on the premises on such day are not so engaged."

Texas welcomes companies that believe in the American constitution and freedoms for all Americans.

Now, this law (section a(6) of the state constitution)  ONLY applies to owner occupied residence but because there is a law it makes all equity lending tricky in Texas. 

@Russell Brazil, my contract says "If Purchaser* defaults hereunder, Seller’s sole remedy shall be to receive and retain the Downpayment as liquidated damages, it being agreed that Seller’s damages in case of Purchaser’s *default might be impossible to ascertain and that the Downpayment constitutes a fair and reasonable amount of damages under the circumstances and is not a penalty." 

Agree with you that OP's rentals most likely constitute only one trade or business, thus he has nothing to aggregate. 

Rental activities qualify if they constitute the conduct of a trade or business (see IRC 162), or meet a rather awkwardly structured safe harbor activity requirement.