New garage speaker placement?

I am building a 24x26 detached garage behind my house. I want to put in a nice sounding music setup. I will be using Sonos for source. Garage to be used for detailing my vintage 911 and small projects. ( think 12 gauge garage on garage journal)
Where can i put speakers? I was planning on inwalls. How many should i put in? What kind pf amplification? ($500 or less) i will buy a chesp sub to to fill in bass.
No. Haha, i wish. But, i'm planning a similar space.

I want to fill the room but not sure where to put speakers. I have in celing speakers throughout my house now. I have heard that putting them in wall sounds better than ceiling.
If this a system to listen to while you work, maybe some powered monitors would be the best way to go. They can be placed on a shelf or mounted to a wall. No need to fool around with an external amp. You would just need a source with a volume control. (ipod, tablet, notebook, etc...)
Your best bet is to go to a music store, like Guitar Center. They have brands like KRK, JBL, Tannoy, Adam, Mackie, M Audio, and probably some others I'm forgetting. To be clear, I'm not saying these type of speakers will be as good, or better than traditional audiophile gear, but for a garage where you won't be doing any critical listening, they should work nicely. I have a pair of Tannoy 502's I use on a computer. I know they make a larger one with an 8" woofer. For your garage, those would probably be best.
If you are willing to hang speakers on a wall instead of using within wall types, and for $500 and something that will sound nice:

Pioneer SP-22lr speakers ($129),
Pioneer A-20 amplifier ($270),
Pioneer makes a subwoofer that mates with the SP22s (i believe ~$130).

All values retail.
For this system you need 7.2 surround; nothing else will suffice! ;)

You may want to reconsider in-wall placement of speakers in the event that you will reconfigure the shop/work area. If you ever move things around within the space, you may want to change the location of the speakers.

Zd542 gives good idea on powered speakers. Another alternative is vintage gear. I have a lovely vintage Nikko stack with some monitors that resides on my oversized workbench.