Are you trying to cycle this tank or are you just planning on changing the water when needed? I would recommend atleast buying an ammonia test kit if your going to be changing all the water. Whenever you get an ammonia reading you know it's time to change the water. Testing everyday after you do the water change is a good way to find out how long inbetween water changes you can go.
Most of the LFS don't know what there talking about, and just because they keep there fish all piled together doesn't mean it's ok for us to do the same. I would recommend getting a hospital tank/one gallon bowl if you planning on getting anymore fish from your LFS. It's best to isolate your new arrivals for a few weeks before adding them to your tank to make sure they don't have any diseases. I know it sounds like a hassle, but I'm sure many of us on here can say we have defeintly learned our lesson about just throwing a new fish in our tanks.
I've always heard ADF's were great for bettas. But make sure what your petstore is selling you is actually an African Dwarf Frog and not an African Clawed frog, which can get really big and eat your betta! If you do decide in the future to get a frog I would recommend getting 2 because they love to play together. Feeding is a problem, so you'll probably have to take them out of the tank a put them into a small cup to feed them. I take a pair of tweezers and wave the bloodworms in front of there face. ADF's can see well and if you don't take them out to feed them your betta will probably devour all the leftovers and they won't get any
