See https://library.municode.com/tx/killeen/codes/code_of_ordinancesChapter 26 is known as "City of Killeen Subdivision and Property Development Regulations."

Your answer would be it depends on a million things.Like the specific property, its condition, location to desirable areas, local STR regulations etc.We would need much more detail to be able to help.

And anything over 31 (some cities do 30 so verify) days is considered MTR and typically has less regulations. - Short-Term Rental (STR) License - Littleton CO - The shorter the stay, normally the higher the revenue but also higher work with turnover, etc.You'll also want to check zoning laws to see if you can legally have it be a duplex if you move out. 

https://www.phila.gov/CityPlanning/resources/Publi...pg 40/41"[1] When the proposed use is in an attached or semi-detached building, the household living use regulations of the residential district to which it is attached apply.

Unsuccessful Property Search: Hours spent on unsuccessful property searches, where no purchase is made, do not qualify.On-Call Periods: Instances where you are on-call but do not actively perform work do not count towards material participation.Meeting Requirements:Maintain Detailed Records: Keep accurate time logs and records documenting your involvement in material participation activities, supported by evidence such as emails and calendar appointments.Seek Professional Guidance: Collaborate with a qualified tax professional to ensure compliance with IRS regulations and to optimize your material participation strategy.I hope this high-level overview gives you insight into what activities matter and ones that do not.

If STR regulations come to the area, my plan is to do MTR and while it is not as much revenue as STR, I should be able to generate a decent return over a 5 year minimum hold. 

1) The regulation 1.263(a)-(f) reads that you're able to utilize it for amounts paid during the taxable year.

At one time this was allowed but is no longer legal or acceptable under RESPA regulations. 

I converted my garage to an ADU and now my main house is considered RSO unit since it was built before 1978. I have been airbnb’ing it less than 120 days which was helping me to work/ travel a portion of the year outs...

Diversification across 3 markets also de-risks my investment if local regulations or micro-factors shift negatively in one market.