The filtration you have it is going to be pushed above its limits with that lionfish as it gets bigger it will then pick of your stock one by one if they can fit in its mouth !!!!
I have a fuzzy dwarf lionfish in a reef tank and I also have cleaner shrimp there is a massive risk that when it grows up it will eat them, but at present it let's them on to clean so I'm hoping that it will not eat them but that risk is there and I'm prepared for it.
My system is a 6x2x2 DT and a 4ft x18"x17" sump running a massive filtration system and my system is no where near fully stocked this is for a reason as it's a reef tank it helps with water quality.
In my opinion remove the damsels , humbugs if that's what you have and the lionfish and change your LFS
as they seem to just be selling you any old thing.
When things go wrong in the marine world it costs £££££ and if you starting in the wrong direction then it will be harder.
What are you wanting from the system in the end a reef or FOWLR
if a reef give us all an idea of what sort of corals you are wanting and we can advise on stock that will fit your end goal