They told you to cycle your tank with fish? OMGosh
I made that mistake with my first tank, a FW goldfish tank, many years ago. Had 1 ppm ammonia, and the fish looked a bit sick. A few days after I bought the fish, I took them back to the lfs and told them my tank wasn't cycled and that I did not want to risk the lives of the fish in order to cycle a tank.
Tank cycling can be done in many ways that do not involve using live fish. One way is to use live rock, and that is what I would suggest you do. Please take the fish back and use LR to cycle your tank instead.
While cycling your tank with LR, test for ammonia and nitrite for the first few weeks. Once both have gone down to 0 ppm, test for nitrate. By that time nitrate will be pretty high. Do a very large water change to reduce nitrate to as close to 0 ppm as you can.
You can then begin to add fish one or two at a time. Add the most aggressive fish at the very end.
HTH
