You will want to increase flow in the tank. The little HOB filter will provde a minimal amount, but nowhere near enough. Figure on 20-30x tank volume ( ~600-900gph) for soft and LPS corals, and 40x or more for SPS (~1200gph). A couple powerheads will be the easiest option for that. Look at the Koralia line for reasonably priced units that will suit your setup, and remember that 2 or more powerheads will always be better than just one, more powerful, powerhead because it is easier to set them up to provide a more random, chaotic flow. Dead spots in the tank are the bane of every reefer.
The HOB filter will give you mechanical filtration and perhaps a small amount of biological filtration, but the lions share of the denitrifying process takes place in and on the live rock. On that note, I'd suggest adding some more. It will, at least IMO, also improve the look of the tank while also adding more places for fish to explore and hide.
Is that the stock light? If so, it will be adequate for a fish only system (they don't care if there's a light at all!), but far from optimal for any but the least light demanding soft corals. Deciding on what your plans are for the tank will determine your lighting options, so if you'll fill us in on what's down the road we can help more with that.
With a tank that size, other equipment is nice, but far from mandatory. I kept a very successful 60g cube for 22 years with nothing more than a HOB and canister filter, a heater, a couple powerheads, and T12VHO lighting. Water changes alone can easily keep things in check for you. Thinks like skimmers and reactors are nice, but not necessary at this point for you.
HTH!