Welcome to TRT
Are you looking at high nitrate at this point? In theory a 50% water change should reduce nitrate by half if you are using RO/Di water to mix up your salt. Once you add fish and inverts that wont hold true as ongoing biological processes will skew levels.
As to stocking start with one and wait a week or two for the tanks biofiltration to ramp up. Figure out ho many fish you can support in tank and compile a list of must haves, then research compatibility and feeding. I suggest adding the most aggressive fish last so the others can establish safe spots.
The short answer in my opinion is that it really doesn't matter if you do 10 or 20, or even 50 percent at this point assuming nothing is out of range. The cycling procedure has you not do a water change during the cycle because you want the high ammonia levels to grow the types of Bacteria you need. Once the cycle is complete and Ammonia, and Nitrite are 0 that restriction is lifted. If at this point you find your Nitrate levels high the water change will help reduce that.
Other than correcting levels that are off, I'd say you're safe to start stocking (slowly)