Maybe I missed the Amonia/or Nitrite spike?
was the rock sold as cured? If so, maybe it just cleared up any spikes that it might have had before you tested?
So now do the 1/3 water change?
eh...i never have done a water change right after a cycle. For some reason i never really have high nitrates after a cycle, so i just dont bother. Some people recommend it..i'm not saying they're wrong or anything, i'm just going by what my own experience w/it has been. But 10 nitrates really isnt that bad. I wouldnt let them get any higher tho, so maybe a small water change would do the trick. I would say only do like 5 gallons or so tops.
How much water change (and frequency) on a BC29 w/skimmer (not sure the skimmer matters on this ?
first thing, yes...skimmers do play a part in how often you need to do water changes lots of times. What skimmer do you have? If its a good one, it should help considerably.
As far as how often and how much to change...what type of tank is it gonna be? I'm guessing it will be a reef tank since you bothered to pay extra to get a tank w/built in lighting? But will it be mostly soft corals or will you be trying to do some harder stuff?
For fish only tanks...you could go a really really long time w/out water changes. Nitrates dont hurt fish, and thats really all that would be accumulating over time. Not like there's any corals that need the calcium/trace elements out of the water, so you dont have to replace that.
If its a softy coral only tank, that might be a little different. But on my 40 breeder, i really dont do much to it and it runs perfectly fine. I do maybe one small water change per month, and i have lots of softies (mostly leathers) and a couple lps and sps. Everything seems fine, altho i am dosing that salifert "Trace Soft" stuff. Is it helping? Not sure lol, but i didnt pay for it so its all good

. I do maybe 5 gallons every water change and its about 45g total (w/sump).
On yours, if you plan to do fish only...maybe 5g every month and a half? Probably longer tho since you've got a skimmer (i'm not running one even).
If you're doing softies only, i'd say do at least one 5g change per month. If you're finding you're having trouble w/nitrates tho, maybe every 2 weeks, or just try adding a fuge.
But if you wanna do some of the more difficult/less hardy stuff, then i'd say at least 5g every 2 weeks or every week even. But dont do big water changes. IMO 5g should be the most you change so you dont mess stuff up. On my tanks...i just let them go and monitor the levels. As long as everything stays well, i see no point in changing anything.