I know envy is not a trait I'm supposed to harbor, but as a guy with absolutely no space in the garage, and living on a postage stamp of a lot, I'm WAY envious of your ability to build out like that. Congrats on being able to do what so many of us wish we could.
I'm surprised one of us hasn't asked the obvious question yet. . . does your wife have any sisters?
As for speakers, there are some quality wireless options out now that are compact. You could stuff them in each corner of the garage to deliver some nice tunes while you play!