Hi there and welcome to the forum.
Do we know the size of your tank? What are its dimensions as well? It looks to me like you picked some fish that appeal to you and were hoping they would get along? Correct me if I'm wrong. Seems like an odd combo is why I ask. If you give us size (gallons, liters) and dimensions we can help with stocking a bit more.
The fish you chose are incompatible. The Pacus get huge. Depending on the subspecies we are talking a 16 inch to more than 30 inch fish that is probably just as deep as he is long. Really has no place in a normal size tank.
Puffers are often recommended for species tanks meaning they are the only species in the tank. And yes many but not all are brackish, slight saltwater, fish.
Think about designing a tank this way:
1. Do you want aggressive, semi-aggressive, or a community tank?
2. Look at regions: African cichlids, south american, asian communities for example.
3. Think about the level at which the fish are comfortable: bottom feeders that sift through sand, middle swimming fish and top feeders. So you get more balance.
Hope this helps.