Most starfish are reef compatible but need high water quality and are very sensitive to changes in oxygen levels, salinity and pH of the water, and cannot tolerate copper-based medications. Best to wait 6+ months for your tank to fully stabilize.
You might want to add another 30+lbs of sand, 60 lbs for a 55 only gives you about 1.5-2” sand bed. That’s ok but 3-4” would be a little better.
Which bio-wheel filter did you get? If it’s the H.O.T Magnum then the micron filter will help in keeping your tank crystal clear, if it’s just a
hob free flowing and not a canister then it will only marginally help. Either way you have to make sure you keep the filters clean or else you could see your
no3 rise.
Clean up crews will most likely eat any dead fish/inverts but if the fish/invert is too large you will need to remove it.
With any additions doing a drip acclimation for 2+ hours will greatly increase your chances of long term survival. As canyon15 said, waiting for 2+ months will help also and give your tank time to stabilize.