Wow! Super lucky to have the luxury of extra space! I can't tell you what to do exactly with your space, but I would suggest to change out your garage door. I love this idea, and I would really like to utilize it when I build! If I can't have it...I'll just be happy that someone else is enjoying it in the meantime!

I'd suggest a shallow bench underneath the window and flank the windows with a base cabinet on one side and a desk on the other. Then open book shelves above the base cabinet and desk. I can't tell what the dark wall is on the one end. The steps need to curve from the door to the wall. A smallish sofa would be great for viewing a flat screne TV and a square table and 3 chairs up against the dark wall would be a great place for puzzles and games. Put a pendant over the table.

Hi, the green is pretty but needs a fresh coat of exterior grade paint {clean and lightly sand existing finish}. Some tall Evergreen Shrubs to hide the electrical components on the left side of the picture, some potted flowers in orange clay pots to keep your plant company on the right side...maybe an iron scroll work art sculpture above the garage door? Cannot provide input to interior without any photos.

Unless you have a very beautiful garage door I would paint it a color that blends with the brick IMO they are all too much in your face as is I loved it when the garage was at the back of the house not front and center