Cycling takes way more than 2 days. Petsmart is full of idiots. First rule of fish keeping::: NEVER listen to petstore employees. 80% are not knowledgeable and are out to make a sale.
You can try to get established media from a petstore to run in your filter, and one of those bottled bacterias to make your cycle start faster, but at minimum that'll still take a couple weeks.
You can do a fish in cycle, but that takes even more time and you'll have to test daily.
Please read up on that before purchasing any fish!
As for the dwarf gouramis, you should have a filter, but what kind doesn't matter. You should get something rated for double your tank size (or close) so that more benificial bacteria can grow on it to keep your parameters more stable.
You'll also definitely want to buy a test kit. I know pet stores will do it for free, but that's A LOT of trips you'll have to make there...buying your own saves a lot more time and gas.