I've gone with guppies and platties myself, but I did check with the LFS that they'd take the fry (for trade or free) so that they'd get good homes. I'm also going to add in three swordtails, too. With the differences in size and species, I do expect fry to be eaten as well.
As for combining tetras and guppies, I've been debating that for two months now: on the one hand, neons (say) and guppies are all rather peaceful, and they were all likely in 7.4 PH water in the LFS. On the other hand, neons and the like would likely be happier in something more acidic. If you're using tap water that is 7.4 or something more neutral, I'd combine the two.
My water is well, and I live in an area with a lot of rock. I have 7.8/8.0 water now, and my master plan of combining neons and guppies seems off. I can't imagine neons liking it that much harder than their natural habitat, and anything I could do to bring my water down a little would only destabilize the tank and tick off my livebearers (guppies and platties). Still, the LFS has neons 5 for 5 yet, and I really like them. (I have a thread elsewhere called Guppy Tankmates if anyone wants to weigh in, so I can avoid hijacking this one.)
With tetras of any kind, I would expect more of your guppies to survive to adulthood, and that might be an issue if you can't find them good homes.
Again because of water conditions, I'm contemplating shrimp for my clean up crew in my livebearer tank. That might be an option for you rather than the cories. I expect a lot of fry and a lot of waste from the livebearers I have (I have 3 adult guppies and 3 platties, and 6 days into having guppies, I got fry). Keeping your fish count down is going to be a good thing, too.