Lucky you . . .a whole house dedicated to sewing!!! :)
Neither the air conditioner nor the heater should pose a problem. However, depending on what part of Texas you're in, you might want to manage the humidity a bit. I'm in West Texas where it's considered high desert and very dry (most years, anyway) :D So need to add a little humidity in the house in the wintertime to protect wood furnishings, ie. sewing tables, cabinets and shelving. If you're in East or South Texas, it's VERY humid which can be pretty taxing on machines so you'll want to make sure the window unit does a good job of condensing the humidity and clearing it out.
Would love to see pictures of your finished "sewing house" :) And congratulations!!!!! :)