Hi, I am sorry to hear about your poor fishies! I actually didn't know what fishless cycling was, so I left my tank for six weeks and then added neons (DOH!)

. Neons are pretty hardy fish, and luckily all mine survived. I think the best thing for you to do is read up on water chemistry, some of the basics I had to quickly learn are the following:
Ammonia - poisonous and needs to be at zero!
Nitrite - Also as poisonous but it means the ammonia is breaking down - also needs to be at 0
Nitrate - is probably at about 10-20 in a cycled tank and isn't harmful iin small amounts, and is a biproduct of ammonia breaking down.
The first thing you should do is buy a test kit that tests all of these, I would suggest you do water changes of 20% daily as any more and you will be removing the ammonia and nitrite your good bacteria need to feed on in order to be able to get strong enough to support fish. You can also buy some products to help you to aid it, I used one called cycle - not sure if it does actually help but like I said my fish survived. And your neons are one of your best fish to start with but they are not indistructable. I would also look into finding a new adisor at your lfs. Also if they advise you to try guppies instead as first fish, completely ignore them, guppies do better in a mature tank, so no less than a couple of months old.
A fishless cycle is hard work, I have never done one and takes a bit of knowledge and research. I would definately take back your cat fish, it isn't likely to survive, I would keep up with your water changes and try and obtain some mature filter media, maybe you could post it on the wanted section and see if someone could help.
Even with fish in it, it will take around 6 weeks to cycle your tank, if not more and you shouldn't have added any more than five as your filter needs time to adjust to the waste load. Also, if you are having trouble, people could help you a lot more if you added your tank size, your ph, decor, nitrite and nitrate.
Good luck.
Sorry, also your fish do need feeding daily, a small pinch will do, try about 6 or 7 flakes.