Nitrates are the end more or less of the nitrogen cycle. You can't have too much live rock, but as you tank cycles, a lot if die off in it can cause a longer cycle. Once you have it established, more live rock typically allows for more surface area, which is usually a good thing.
Yes big water changes, minimal food, macro algae in my sump. I just did a 35% water change and it didn't touch my nitrates! I have 4 fish, 2 shrimp, and some hermits. Sorry I'm just tired of getting nowhere!
that's odd, maybe try another test kit or take some water in to a LFS to confirm the numbers...I would try basting all the rocks with a turkey baster to blow detritus out and then do another 35-50% WC, sucking out as much detritus as possible
I would also suggest getting an RODI if you are going to keep coral