Severe roof damage that now let’s all elements inside the home.

My plan was going to be to take a heat gun to the old paint, replace any wood that might need replacing, and then give it some nice fresh pain. 

The bottom unit doesn't have it's own independent hvac system so AC and Heat is shared with the first floor of the property.

I don't know about the layout of your house, how well-insulated it is, or your climate, all of which factor into what makes sense for you.A heat-pump is basically an A/C that can "run backwards" to heat the house.

Looking ahead, we feel we need some guidance on how to leverage what we have so far, taking into account all the different elements of investing: Understanding markets, Taxes (across states), HELOC's, 401k's, etc.

And some repairs were quickly addressed when they were priorities (heating, leaks, etc.)

When people start moving here in droves it feels like a flood and has affected the housing stock accordingly with our inventory down to 1 month.I suspect many will also come from other parts of the country especially parts of the country were they dont think twice of heat humidity thunderstorms tornados etc.. all things the SF bay area has none of  LOL. 

I don’t know a lot about HVAC, so I was hoping to get some ideas about what to do to get a cooling and heating system for the living room on the first floor.Thanks

Just to name a couple elements of differential strategy.

Know your options, as there are lots of elements to this.