Here we go..... again
Live Rock : Not needed, optional. You have filters; you can use those to start
A Good Protein Skimmer: Not needed, optional.. same as above.
Minimum you could use what you have. Bare bones: Your Fluval's or HOB
are enough ( I would use the can's). A powerhead or two in the 55 along w/ the canister return. Sand (optional), LR
(optional), Skimmer (optional), sump (optional), expensive lighting (optional).
One step up. Sand bottom , a few LR
One step up. Lotsa rock for filtration, consider ditching the can's ..or keep em
One step up. High end lighting for inverts and coral
One step up. Overflow/Sump/Ref
Pick your price point and go from there...
There are 3 gotta haves. Water, filtration and heat.. EVERYTHING else is optional
So bare bones getting started you have everything you need. If you want to dip your toes in the water.