Garage remodel: can I leave garage door in and put an insulated wall in front?

There are kits you can buy to stuff into most traditional garage doors and get a decent amount of R value into the door (not as much as a wall, but not 0).

If you're wanting to block the door and insulate, you might just be able to rig up some 2x4 framing within the doorway, insulate and do something simple like concrete board outside (I'm not sure if there's any code that would prevent this, so check local codes before doing it). Done with screws, it could be dismantled if you change your mind.

I wouldn't brick the door off since removing the garage door in a permanent way like that might impact the resale value later on.

I had a similar issue but in a cold climate. I thought about putting an insulated wall inside and under the garage door. making a small space to heat and be completely insulated. In the end, I found it was easier just to insulated the door. you can take off the back panels and spray poly in them. it's not a big job.

The major issue i found was having to build a dropdown ceiling below where the garage door opens and being able to insulate that. Depending on the span of your garage you might need 2x6's or even 2x8's to pass code if you have no support in the middle. maybe some sistered. This is going to be costly and you lose too much space overhead as you are already down under the "ceiling door area".

I had a neighbour whom finished his garage. He built a wall 2ft in front of the garage door and had the whole garage insulated. Garage door still operated by the opener. That way his garden tools still had a spot to hang up. Probably a bit of framing involved.