You don't necessarily need fish to cycle your tank. You just need a source of ammonia from a lfs and administer it at regular intervals until the tank stabalizes. If you want to do it with fish, livebearers and danios are the fish of choice, at least for many aquarists on this forum.
Now, you might want to put those guppies and corydoras together in a ten gallon tank. That way you get fish in different strata of the tank. Make sure you get algae wafers and shirmp pellets for the corydoras. They're not pooper-scoopers, ya know.
With the guppies in the ten gallon, you can set up a five gallon tank with a sponge filter and aertaion as a rearing tank. That way you can save more fry and feed the fry properly.
Bettas should be fine in gallon tanks. It's better to have them in those big bowls--it makes them happier than in those cramped cups that so many people keep them in.
The ADF should be a good additon to the betta tank.
You can get info on them in the amphibians forum on this site.
They need live or frozen meaty foods, so as long as you can get blood worms and brine shrimp...
Dwarf puffers are very territorial. I kept three together in a tank and one died from the stress of the move from the lfs. Then another died because it wouldn't eat. Finally, the one stayed alive for about a month, during which time it shredded apart the antennae of my ghost shrimp. It is suggested that one puffer be kept per 15 gallons of water. Not sure if that's true, though. You should be able to find answers in the oddballs section here.
HTH