That's correct.
NiMh's are 1.2 volts per cell.

Robert,

The only real problem I see is the ESC rating. My Slow Stick came with the EPS-300C "D" motor gear-box, with an 1180 prop. I run it with a 7-cell NiMh 1300mAh AA sized pack, and it draws 8.3 amps at full throttle. Start-up current is a bit higher, but the ESC should be able to handle short duration spikes. If you are in fact running an 8.4V pack, you might be OK, but definitely not 9.6V. The fact that current rating is a function of thermal dissipation, and the ESC on the Slow Stick is out in the open and convectively cooled by constant cool moving air, the ESC may handle more than rated, but why push it? Even though you may typically run the SS at 2/3 throttle or less, you will in time diminish the life of your ESC. When it goes, you may lose 100% control of the plane. Again, it might be fine for a lifetime, but when starting out, it a good idea to aim for a reduction in variables.

Almost all ESC's have battery eliminating circuitry (BEC), which means that it actually provides power to your receiver and servos by regulating down and siphoning off your flight battery pack. It only connects to one point on the RX, namely the throttle servo connection (Ch-3 for Hitec). This is generally prefferred to using a separate battery pack as you mentioned, although you're right, the Slow Stick could handle the extra weight. I've seen set-ups where a "Y" connector is used to specifically power one servo from a separate pack on larger planes, but if you plan to use a separate pack, I would plug it into the battery port on the Rx, and probably disable the BEC connection on the ESC connector to the RX. I think cutting the middle wire would do it, but take a look at the ESC and Rx documentation to make sure. Disabling the BEC may not even be neccessary here, but with 2 DC sources, the ESC may do something screwy with the auto cut-off. Again, not sure, but I would fly without the separate pack anyway. There's no reason to add the extra weight, even if tolerable.

I think Ken answered the CG question. I've only had my SS for about a week, and I made the sucker really tail heavy doing tail-feather mods, epoxy embedded carbon fiber, etc... as well as the other "standards," balsa in fuse, epoxy and fiber-tape everywhere. The finished weight, with battery and very heavy Hitec 7-Ch PCM Rx is ~20.5 ounces. I balanced it as the instructions said, and the battery is right up against the back of the motor. I had to change the order of the mounting pieces. Anyway, I've only flown it once. It took off from loose dirt in exactly 9 ft, in light wind, probably too much wind for a pilot of my ability. The plane flew a bit loopy and tried to go vertical whenever it got the chance. I think Ken (And many others) are right that the CG needs to be a bit forward of where the instructions say. I'm not sure how much, as after about 5 mins, I crashed it directly into the ground. I have to say, this thing took a header like a champ. I literally stuck it head first into the grass on a soccer field, and the only thing that broke was the prop. Of course everything slid down the stick, as I didn't fix them in place in order to tune the CG, but that's it. A crash that only cost me $1.75.