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.

So while I don't know costs you will want to pay special attention to insulation to control the temperature (especially in Florida).

You can ask, but expect to offer lower rent or some other form of compensation.I don't think you can dictate at what temperature they keep the thermostat.

I have just always wanted to have the tenant have some ownership in what they use, as all too many times I see the thermostat set at 80F in the winter, with the open window used to moderate temperature!!

You will be up against the willingness for tenants to hunker down with the temperatures drop but if as @Dawn Anastasi states, if you are offering a quality product you will have no problem. 

I would start with some good land lording practices, some DIY prevention, and in parallel a call to a mold remediator.Good land lording practice would be to explain humidity and temperature combine to make mold grow.  

With prices up by that much this quickly, I'm sure you guys can understand why I'm being cautious about jumping in without checking the temperature of the water first!  

1) Don't buy 2nd's unless you know what you're doing (which you probably don't).2) Don't forget to check for all the other liens that might stay with the property, but do make distinctions between liens that stay with the property and liens that don't.3) Don't by sight unseen unless you're trying to place a ridiculous amount of capital and you can make it up on volume.4) Don't buy without determining occupancy status and the "temperature" of the occupants.5) If the guys that show up every day are bidding on something, you probably can't make it work on your margins.6) Don't get emotional.7) Seriously, don't get emotional.

In the efforts of finding fix n flip deals in the various small and large communities in Weld and Larimer counties, I'm curious if anyone can recommend a solid wholesaler(s) in these markets?  

its hot always.. temperature and just business attitude.