The above two posters are very much right IME.
Additionally, I just wanted to pass on some warning: Snappers honestly will not let anything else live in there. Now matter how much you stock it with fish, they likely won't survive to a point of being sustainable. I've kept snappers, and seen them go through 6-10 fish the size of their head and still be asking for more. They're pigs.
That being said, they are pigs with a lot of character. I would highly recommend them, but again you really aren't going to be able to have any other fish, turtles, or frogs (or even slightly smaller snappers in some rare cases - I've witnessed cannibalism in the species). Furthermore, as has been mentioned, they will rarely if ever be visible, and the filtration requirements to keep them inside are unbelievable (though with an outdoor pond, I don't think you'll have to worry or filter much at all unless you want the water to remain crystal).
Personally, I would try to keep it relatively snapper-free. I think you'll get more enjoyment out of the pond as a whole. Stock it with lots of fish and basking turtles, and then just sit outside and watch your macrocosm of an ecosystem sustain itself

.
Just out of curiosity, do you live in a region where you would have to worry about winterizing it? and if so how to plan on doing so?
One last thing, if you want a neat experience for turtles: this May/June most turtles will be migrating to the opposite side of most roads (haha) and laying eggs. If you happen across any turtles laying, dig the eggs up within about 24 hours and place them carefully in a container with some sand (keep them right side up, though the embryos usually haven't attached to the egg wall yet, hence the 24 hour spec). After laying them all out in a bed of sand, loosely cover them with some more sand about an inch or two deep. leave that container in a safe but monitored place until around early august, and you should have a bunch of baby turtles to stock you pond with. And honestly, that's a very rewarding experience. That's where I got my knowledge with snappers (and others) because we live on a water front and they lay in our driveway all the time. But through the year, the dirt in the driveway gets really compact and there's no way the babies would be able to dig out. So we dig up the eggs, hatch them, and release them a few days later. I know it may no be great for the environment, what with the 100% success rate of them hatching and getting to water, but we feel bad about having a driveway essentially on THEIR breeding grounds.
Anyway, i digress, best of luck kearth.