If it's a real dwarf puffer, they're completely freshwater, and only get to about 1". They will not ever take flake or dried food, and you have to feed them bloodworms and mysis shrimp. Like all other "beak" fish, they need to grind off their teeth, but luckily, bloodworms and shrimp are good enough to do the job. They're messy eaters, so either have the tank heavily planted or have a great filtration system without much flow, because they're not the greatest of swimmers.
And as for a cycle, why not just take a sponge filter and set it up in another tank for a week, then plop it in the 10G tank and let it cook for a bit, then throw in your fish?