Couple of cycling related questions

Hi everyone, my partner and I are new to marine keeping and in the process of setting up our first tank - a 90G including sump. On the last batch of LR we bought we have found a couple of mushroom corals, a whole gang of tiny feather duster style worms, a hairy legged crab (think it's a gorilla crab, but no idea where it is so don't tell me to get it out!!), a tiny brittle star and several snails. We've added all live rock + about 30% live sand, filled up with water (SG 0.026 at present) and have started adding a pinch of flake food a day to kick start the cycling process. What I'm concerned about is are all the critters inadvertently added with the LR going to die as the cycling process progresses?? If the answer if 'probably' is there anything we can do to try and prevent this? And finally can we monitor the cycling process with just ammonia and nitrate tests or do we need to buy a nitrite one too (we will be testing other things as we progress like Ca and Alk etc but for the moment...)?