Ill make some predictions going off these assumptions:
1. all the live rock is just like that and none of it is white or gray
2. the live sand was either caribsea arrive alive wet pack, which is ready ive used it for 12 yrs, and that means the tank can process a reasonable bioload or
3. the live sand was not live, its inert material as of yet, to be matured, so your max bioloading is set by the lbs of that cycled base rock used.
That being the case, you can absolutely add shrimp, 3 shrimp, cleaning ammonia, or a a couple easy corals and just get started testing this tanks cycling no more.
It is very hard to trust a tank especially when inside the first rulebreaking thread lol
any tank can have its nitrification abilities tested at any time, add some ammonia and check back in 24 hours to see it at zero. when you do this on 1000 tanks then you w trust! ha lol./
if your live sand was caribsea or similar arrive alive wet packs, that alone means your tank can process any reasonable bioloading. You indeed have some pre cycled rocks, so until you really drive up that ammonia its not going to do much. They are simply filtering that which you are putting in to test them.