A picture is so valuable....
The denitrator, although not common, should prove to be very effective. There are a lot of old school hobbyists who used these, primary as a method to keep nitrates low on systems with biological filtration. It is probably not needed, but won't hurt.
Your sand bed is nice, but you need to smooth it over. I know it looks nice as it is, but you want equal depths across the aquarium to encourage the correct bacteria growths. The ideal depth is 4-6''. Any areas under 4'' tend to become long term nutrient traps and contribute to algae growth. For the record, under 1'' is also an option.
Over the long term, and preferably sooner than later, you will want to remove the canister filter. Any form of mechanical filtration in the marine hobby can cause long term problems. Canister filters, being very effective mechanical filters, can be highly problematic. The act of mechanical filtration traps organic waste, preventing it from being removed from the water (by the protein skimmer). These organics break down the carbonate buffer system and indirectly add phosphate to the water. The regulation of alkalinity and calcium are your biggest long term concerns, and you are making this more difficult with the use of a canister filter.
The protein skimmer is optional for the first 1 or 2 months, but it is critical that you obtain a high quality skimmer ASAP. You do not necessarily have to have a sump system. You can use a hang on skimmer, especially on aquariums under 55 gallons in size. Adding a skimmer is far more important and urgent than a wavemaker.