No, you are not going to hell or any other theological or mythological place for people who are concidered "bad" and there is nothing sick about raising your own food for your animals. Many people raise their own food for their animals, It is more economical-and one knows what is in the food. Usually when people raise food, it is grown in its own tank, usually species only and usually doese not consist of fancy guppies and mollies.
You can always sell the fish, for many people state problems with fish feeding of axolotl, especially if the fish is alive. Axolotl are quite slow and lazy so if you planned on Mr. Axolotl hunting down their fish, it just will not work like that. Maybe he will get lucky once or twice. As for axolotl in a self sustaining ecosystem, they need a lot more care than that. It is hard to reproduce a system such as that in a little 20 gallon tank. Even in larger man-made ponds, it takes time for everything to get settled and things do change. Well, you did set up a nice tank and you are using plants and it looks beautiful. Shrimp farms are fun, and is a bit safer than fish with axolotl. Just keep an eye on things, especially with the fish.