Preditor Tank

I have good news. In 6 moths to a year, I will be upgrading to a 100g. I will move my 40b and would like to turn it into a fish only tank, with a snowflake eel, and dwarf lionfish, and a possible puffer fish. I would feed them live ghost shrimp, that I harvested at my boat dock and quarantined, for food. How should I set up my 40b for a snowflake eel, lionfish, and puffer fish? what should type of Substrate should I use? How much? How much live rock? Etc...
Also, Please don't tell me a snowflake eel and lionfish need a 50g. My friend has kept a snowflake eel in a 40g without any troubles for 5 years.