Well, let's look at your choices:
The mirror ball is a bit on the large size, but I expect you're talking a permanent thing, so in that case, size doens't matter. And if it is permanent, bigger is better. Point some LED Par36's at it and regardless, you've got a good thing right there. If you want to spice it up, aim different colors at the mirror ball. Also, use a properly rated motor, you're gonna want to spin that mirror ball.
Exciting the dance floor? Yeah, Par cans are nice to flood and wash. Not the greatest, but a tried and trie thing. You'll want to use something that is going to penetrate far enough, so definately Par38's are out. Par46's are a bit narrow. 56's and 64s would be the way to go. But, if you want a wider wash, perhaps an LED Punch Pro might be the ticket you are after?
Centerpieces is a matter of preference. I would get at least 3. The Sunray III is a nice color mirror-ball like fixture, rotating at 6rpm. but I know you're going LED. Mine is the older halogen. Been a great item for me. Another I recommend is the Mystic. It's has a really large throw area, super bright, so fog isn't a big deal. The Sunray III looks better with fog since it's a moonbeam fixture(whatever that means). A Vertigo is also nice, but is small, so you might want two of those for coverage. A copter-type fixture would be nifty, or those rotating ball/globe ones.
I mention multiple centerpieces because some have duty cycles. You can rotate between 3 or 4 lights every 10 minutes and ensure ample rotation. You could do it with 2, but if you have 3 or more, it's better variety for your guests.
If you plan it right, and it's pretty easy to, you'll have yourself a system that if it looks great without fog, it should look cooler with fog or haze. There are some lights that simply suck without fog though. What I'd do is really call up or fill out the form on the ADJ web site and order their latest product DVD and print catalog. Watch the DVD, follow with the print catalog. Take notes IN the print catalog of things you like and don't like. That will narrow it down as to things that you think are going to work for you.
Two things you need to take into consideration:
Mounting. Are you going to install it right to studs or at least some sort of structural framing? Or are you going to install trussing? I recommend trussing always, even if the trussing is mounted to the studs or joices. It's a more optimal mounting method and ensures adequate ventilaton.
Power. How much power you need up there? Are you going to have proper power installed?Dedicated circuits? Running power from dimmer or power packs? Think ahead and think safe.
Control. Crap, that's 3 things. Are you going to go DMX? Dimmer/power packs? How you gonna get signal up there? Use a DMX terminator, use DMX cabling. Heck, you might even install an XLR outlet for the cabling just to neaten things up and help facilitate upgrades later on.
Catalog and product DVD and some time to view and take notes. Good stuff!