I suggest you use workout mats or horse mats on the floor, they will still be sturdy enough to drive a car or do some kind of winter maintenance on a vehicle in a jiffy if you’re a handy dude and they absorb low and high fairly decently especially the textured ones with the million ridges in them. On the garage door I suggest you implement the double layer method to insulating the door. (It’s like a poor man’s insulation method that actually far outpaces normal insulation methods I think a channel called garage door man or something has a video on it) anyways itl help with noise coming from the outside in as well as help with reverb and other unwanted acoustic noises for a fairly cheap solution.

Lastly I suggest if the roof of the garage isn’t finished. Which It probably is since your floor plan looks like there’s a room above it I’d finish it and use mineral based insulation as much as you can as fiberglass isn’t great for sound. You really just need to stack porous mass as much as you can and try and fix the squareness of the space. A great way to do it tastefully is to put corner shelving that acts as obviously a shelf but secondly to avoid those nasty reflections. You’ll want something on the flat surfaces as well. I recommend building those acoustic sound dispersing wall art things out of blocks of wood glued to a frame. If you stain and paint it with a gradient they look beautiful and would fit the garage asthetic but this is all just my opinion. Just be blessed you have a wife that recognizes you want your own space as some of us unfortunately don’t have that