I'm assuming you have a standard 45 Cube; 24x24x18?
If so, the XR15 won't be enough light. Not saying due to doubts, but from personal experience on the IM Fusion 40. Exact same thing with my friend in terms of light, tank, coral. I'd recommend adding another if all possible.
Other than that, simple water changes will be completely fine for the most part. Not until you're heavily stocked will you be needing to add 2-part to keep up with depletion. I'd say 10% weekly water changes would be sufficient enough. Would also replace trace elements obviously.
I'm running a Reefer 170 with all SPS. Aside from heavily feeding, water changes seemed to cause my growth to explode into almost noticeable growth daily. Sure I dose 2-part. But it's only 1.1ml a day for each. Keeps my Alk/Ca exactly where I want it st 7.5dKH and 420ppm.
Other than that, it seems as if you're on a good track man!!