My parents ran the piping and receptacles but never got the vacuum for it

I think most standard garages are 20 ft wide with a 16 ft door. That's considered a 2 car garage.

It isn't. Well maybe if you have two Prius cars.

In our current house we did a 24 ft wide garage. It EASILY and COMFORTABLY fits a Camry and a F150 side by side with enough room to open any doors.

Don't go less than 24 ft wide for a 2 car garage. Then, install either two 9ft wide garage doors or one 18ft door.

Don't install the highest end HVAC system but don't get the cheapest either. 14-16 SEER is plenty efficient. If you get into the 16 SEER units you may be able to get a variable speed compressor which will save a little money and possibly increase comfort. But if the price is much higher, a 14 SEER is fine too. With living in Houston, it'll probably be running at the max anyway more than half the year.

Install quality is more important than brand.

Spray foam insulate the entire roof...it will pay for itself.