Let's talk in par and not in watts.... Watts have to do with consumption and nothing to do with light output. LEDs are a perfect example of this.
I would guess at minimum 100-200 par for lower light acro's.
"Deepwater acro" is a term for describing how an acro looks, and normally has nothing to do with how much light it needs.
Why not grow branching/plating montis, stylo, and pocci?
I'm guessing deepwater low light fish tank? IMO soft corals would be better suited for this biotype.