Honestly, I do not like most of the plans you are making on these fish selections. At best you are pushing your luck.
Mixing a predator such as a Dwarf Lion in a small aquarium with a Flame Angel is a stress factor for the Flame. There is just no reason to intentionally cause stress to marine aquarium fish. A Singapore Angel is an extremely difficult species, and needs more room to thrive than you can offer. There is no such thing as a "mellow" Trigger fish, especially in this tank size. And finally, the only Puffers which would have adequate space are the Toby puffers, so hopefully this is what you have in mind.
Sorry, I can't support these ideas when long term success is considered.