First of all, here are a couple of websites that give a lot of info:
http://www.dtmag.com/dive-usa/locations/LakeOuachitaAR.html
Lake Ouachita, Arkansas | Scuba Diving Magazine
There are more websites included in the answers below to some of your questions:
1. What are the water temps?
Apparently, there is a distinct thermocline at 40'-60'. Surface temps tend to be warm, but drop approximately 20 degrees after the thermocline. One website recommended a 3mil wetsuit at lower depths, and a 7mil if you intend to dive deep.
2. What is the depth?
Depths vary, of course. There are plenty of places where the depth is in the 120' range. The deep side of Crawdad Island is 180' so there is potential for those who are interested to do some technical diving.
3. How many tanks should I bring?
I don't know what to tell you about the number of tanks to bring, but I plan on bringing two sets of doubles, 80cf of O2 and 80cf of 50%. We are not going to get fills at the lake as the only fill station closes the last weekend in Sept. We'll have to drive in to Little Rock to refill if we're interested in that, but I don't think it's all that far. Hours of operation for the shops (and there are several) are 9-7 on Friday and 9-5 on Saturday. Here are some of the shops' web addresses:
http://www.ricksdivecenter.com/center/center_index.html
Schedules for the Little Rock Dive Shop
http://www.diveshopii.com/
4. Rec or tech?
Personally, I don't care and am happy to leave this up to y'all, but it sounds to me like we can do both off the same boat depending on the location. For example, one side of Crawdad Island is at technical depths while the other is within recreational depths. I don't mind just doing recreational depths, however. My understanding is that the crystals at Zebra Rock are at recreational depths anyway and that's what I'm going for...besides the party of course!
There is also the Geo-Float Trail, a 16-mile, water-based trail created to help shed light on the lake's natural geological formations. Many stops featured on the trail...Zebra Rock, Whirlpool and Checkerboard Point to name a few...are some of the lake's most popular dive spots. Local marinas carry brochures of the trail.
5. Any shore diving?
Yes, there is. Not a lot, but
the main shore entry for divers is at the far end of the Blakely Mountain Dam. A long series of steps lead from a parking area down to the water and then continue deep into the lake's depth. From the submerged stairway there are cables laid out in a path to a series of sunken boats and vehicles at a variety of depths. This area has some of the clearest visibility in the lake with no current from the hydroelectric dam. The rock face around the dam can reach about 190 feet deep.
6. Where will we be diving?
Well, Zebra Island (#49) and the dam are both on the east end of the lake, http://www.lakeouachita.org/images/lake-ouachita-map.jpg, near the State Park. This is where I suggest we camp also. More info on the park can be found at: Lake Ouachita state Park near Hot Springs, Arkansas ? popular fishing, camping haven.
7. What about boat rentals?
We can rent a 21' pontoon boat at the marina in the State Park for $175/day + fuel. Divided by a half dozen folks that's less than $30/person plus fuel, which shouldn't be too bad with the 50hp outboard that comes with it. Once we get another couple of folks committing I'll see about reserving campsites and a boat.
8. Are there some motels close by?
There are motels and resorts all around the lake. You can camp at the park or you can rent a cabin there. See the URL above for the Ouachita State Park. There is a link to prices for camping and cabins. If you would prefer to stay in a motel or hotel check out this website: Lake Ouachita State Park Travel Guide - Top Hotels, Restaurants, Vacations, Sightseeing in Lake Ouachita State Park : Professional Travel Guide. They point you to several places you can stay on the lake. This is the beginning of their offseason, so I would think prices would be decent.
Any more questions ask. Sign up for the poll too! I'd really like to have a few more divers for the boat. Most importantly, don't say you're going to come if you're not 100% sure. If you commit we'll expect to see you there. 
