RSM tanks should be able to keep sps corals easily. They are built with what you need. Some things are added for convenience, not a necessarily needed.
IMHO it comes down to husbandry - tank chemistry. Once you have good light and random flow in place, it comes down to keeping low nutrients, chemistry, and experience/knowledge. And this is gained over time by allowing the tank to stabilize and building up your knowledge of what is needed and how chemicals and corals interact.
The lighting and the current should be fine in these tanks. Adding additional light or current if fine to add if you feel you need to, but not necessary. Make sure you keep the pumps clean of calcium and crud buildup (soak in vinegar) and keep the lighting replaced as the T5HOs do get old over time. Regular 6 month maintenance goes a long way in keeping current flow high and consistent.
I just recently added a wavemaker pump (couple of months ago) b/c my corals are growing into and over each other that they are cutting off current to each other. I have a full tank of corals and up until now I didn't need additional pumps. With a fill tank of corals growing into each other and cutting off current to each other I felt I needed to compensate or let the corals choke each other off. But, my main reason for going with a wavemaker instead a pump is to create random flow. I didn't want any coral to get blasted with one directional flow. It is not healthy for corals to be blasted everyday in the exact same way. If you see any polyps pushed over to one side, you have too much one directional flow. I also turn off the wavemaker at night, it only runs when the lights are on. It is on a timer to kick on and off with the light schedule. This allows both the corals and fish to have less current to fight against at night, gives them a little relief. With the additional flow of the wavemaker, which creates a surge, it hits all the corals in the tank regardless where they are located b/c the wavemaker forces the entire water column to move in a back and forth way (surge). This allows all corals to be forced to move with the back and forth flow no matter where they are located.
As for dosing, I went a couple of years on water changes alone. Over time I increased the volume of water changes to compensate for Ca and Alk used. It got to the point where I had to dose or increase water changes to an amount that I didn't really want to deal with. After dosing by hand for a long time, I broke down and bought a dosing pump. Sometime after that I noticed that the corals were not only taking in more Ca, Alk and Mg, but other elements. So, tested that elements to determine what I needed to replace and looked into brands and methods to do so.
My advise is to buy the testing kits for elements before buying the chemicals. Test to make sure that you need to dose these. If you have a small amount of sps in the tank it is likely that water changes will do the job for replacing the elements used by the corals. Testing the elements will tell you if this is the case. If by chance that water changes aren't doing the job, then start to dose those elements that are being used. You don't need to spend $$ and dose elements unnecessarily. Also make sure that the Ca, Alk and Mg you are adding doesn't also contain elements. You don't want to double dose.