Not sure if you saw my old thread, but I had a 25gal with pretty much just a powerhead and lights (and a filter pad).
https://forums.saltwaterfish.com/t/331874/my-temporary-25-reef-thread-56k-careful
You'll have to keep the bioload light. Most of the filtration will come through water changes. The 25gal was pretty heavily stocked with corals, so I had to do them more often for elements before the nitrates got high.
We actually have a 10gal running we quasi-turned into a frag rack/tank. Just a HOB filter, PH, and light. It's a 65watt PC from HD. The pics came out a bit blue, but it's not bad. Won't be able to keep SPS (they turn brown cuz it's 6500k), but still getting our feet wet. Zoa growth has been awesome though...