There are a lot of rules such as deadbolt laws, carbon monoxide laws, etc. that are not on the lease, but are Texas law.

also missing a cover- Smoke/Carbon detectors repair/replace needed - Sheetrock to be installed above boiler in attic - Rusted main sewer pipe - Sump Pump needs to be repaired - Master Bath Tub and upstairs hall bath sink slow drain, loose Toilet, broken vent, missing light bulb - Laundry Dryer venting replace for ribbed exhaust vent, missing GFCI- Windows - some missing grill, some hard to lockShould I be worried about some of those items?

It's HEPA, carbon, and UV-C.

id make sure the iron filter is working, then put a whole house carbon filter (not expensive but you’ll need to change filters regularly) after the iron filter to eliminate bad odors.If you go with one of the National Franchise companies, they will hammer you on the price.  

Interior Air QualityBathrooms must have a window that can be opened or must have other adequate ventilation.The unit must be free from dangerous pollutants, such as carbon monoxide.8.

They also applied carbon fiber to a crack in the foundation.

I am renting out a single story single family home in Texas.1) do I need just 1 carbon monoxide detector (I already have multiple smoke detectors)2) house was built in 1977, i’m not aware whether it has a lead paint or not, is there anything else I need to do other than providing the rentee the pamphlet on the lead related issue?

Emergency escape in the bedroom, proper ceiling height, smoke and carbon monoxide detectors, proper permits, zoning, etc.  

Tenant was provided with a few fire extinguishers, two carbon monoxide cum smoke detectors which were affixed to the wall.

I was just inside one of my units fixing some plumbing, and I noticed they had taken down 3 smoke alarms and the only carbon monoxide alarm.