Rusty-
Like Dick said, make sure you get them up and away from the street. I would try to get them at least 10 if not 12 feet above the sidewalk and I would probably use some long carriage bolts to thru-bolt the mounts to the wall (if the wall is cement block or something sturdy like that). Of course, the higher you get them off the sidewalk the less concerned you need to be about people prying them off the wall.
From an installation standpoint, it is tough to beat the JBL Control 25, 28, 29AV, and whatever others they have that use that internal ball mounting scheme. Your Average Joe has no idea how to remove the mount from the speaker. However, there are plenty of other options for small installation loudspeakers from all manner of companies from Bose to (yes, even my employer) Peavey, and they all offer different sorts of brackets for mounting the loudspeakers. Whatever loudspeakers you choose, you may want to consider going the route of a 70V loudspeaker system so you can just string all your loudspeakers together and not have to do a complicated mess of wiring. I would strongly recommend creating a string of loudspeakers for inside the shop and another for outside so you can put a 70V attenuator on each to adjust the levels independently.
Regarding the amplifier, I would expect that you just plan on running a mono system (that is the way these kinds of things are typically set up), so your basic installation amplifier should be sufficient. Something along the lines of a Peavey UMA series is usually what is used in these situations. There are comparable products from Bogen, Toa, Crown, and yes even Behringer. This is the sort of amplifier you are looking for:
http://aa.peavey.com/modularmixeramps/uma1502.cfmYou can usually get them in all sorts of wattage sizes from 10 watts to typically 150 or so watts. Then you should add two attenuators like Atlas AT-10 or AT-35 (depending on how much power you need for each zone) to allow you to turn each zone up and down individually.
Good luck and have fun out there!
(edit: I spellz gud!)