I'm not an experienced .410 guy. However, shotguns are shotguns. 7 1/2 shot is 7 1/2 shot, whether it comes from a .410 or a punt gun.
Pellets hit doves one at a time. Even with a 12 Gauge, only a few pellets hit the bird once you're past a few yards. There's really no such thing as a load that's "too light."
Note that the .410 payload is about half what you'd shoot in a 12 Gauge. That's really not bad; there are plenty of pellets out there if you're used to the gun. 8 shot has 410 pellets per ounce. 1/2 ounce still contains 205 pellets in the pattern; 11/16 contains 282 pellets. You ought to be able to kill a dove with 200-280 pellets, right?
http://en.wikipedia.org/wiki/Shotgun_shell
The real difference is that you might need a Full choke to get the same shot
density going through the air as you can get with an Improved Cylinder choke in a 12 Gauge. That makes the .410 pattern smaller, so there's less slop: you have to
hit the bird with the .410, not just rely on the bird intercepting your big cloud of shot from an open-choked 12 Gauge.
11/16 oz. through that little bore will give a pretty long shot string, especially if you use a tight choke (which you'll have to for long shots). But is that bad? Probably not. You might be able to open up the choke a bit with a bit more shot.
I'd pattern both rounds, and see which one patterns more consistently. The 1/2 oz. load probably will, but maybe there won't be much difference.
Then, go shoot some clays with the gun. That will give you the best feel for what it takes to get a few pellets on target at a given range, IMO.
If you can, set up a thrower, or find a clays range, with overhead passing shots, if that's what you plan on shooting. You may find that the gun is "magic."
Also, experiment with 8 vs. 7 1/2 shot and clays farther out. It's a tradeoff between pattern density (8 is better) and retained energy (7 1/2 is better). 8 slows down sooner; 7 1/2 has fewer pellets in the pattern.
Good luck! It should be fun.