It was aparticularly cold winter with temperatures below zero.

Wanted to temperature check with the community first, though, in case I'm missing something.Bit more background:I'm out of state, but had an investing partner (he didn't have equity in this property) who was acting a project manager for me who confirmed my estimate of $35-40k reno in under three months.

In Northern climes, heat pumps are less effective, but at your latitude(I'm assuming the building is in Texas,) heat pumps are quite effective, and they can have an electrical resistance heating element added in case the temperatures drop below the point at which heat pumps cease to be efficient.One large benefit is that if the tenants pay their own electric, using heat pumps will put the cost of heating and cooling on the tenant- no need to initiate a RUBS system or utility surcharges.

Birmingham, Alabama has a warm humid temperate climate with hot summers and no dry season.Over the course of a year, the temperature typically varies from 33°F to 90°F and is rarely below 20°For above 96°F. 

It lets each individual maintain there own preferred air temperature.  

Mask mandates, temperature checks, only one family member could go into the grocery store at a time, shoe sanitation at the entrance of most buildings and stores, naval forces blocking access to the beach so crowds couldn't enter.

I had two mold remediation companies come and look at it and they both said it is due to the temperature variance in the winter from the craw space to the bedroom. 

In other words, guests will only be able to control the AC between your locked min/max temperatures, but they would not be able to change to heat mode.

NEC Article 394.12 (5) Uses Not PermittedHollow spaces of walls, ceilings, and attics where such spaces are insulated by loose, rolled, or foamed-in-place insulating materials that envelopes the conductors.Blown-in, foam-in or rolled insulation prevents the dissipation of heat into the free air space, resulting in higher conductor temperature, which can cause insulation breakdown and possible fire in the insulation.

Will use that to check the temperature.