If one fish has ick, than the tank is contaiminated. But give yourself, and your fish some room. Work in a calm fashion.
Set up your QT. Use distilled water. I would not use water from your display tank. I would run your QT for 1-2 days, with temps at around 80 degrees. Try to match the SP and pH.
Acclimate your ick fish first. Use the method described on this board. Give him a day. Then introduce the other fish, one at a time, with acclimation. Be generous with the food. Feed as much as they will eat within 3-5 minutes, 3-4 times a day.
The QT will be a boring place for fish coming from your display tank. So food will be their big reward.
Start the hypo. No rush, since your display has to remain without fish for a month.
You have no sand, no LR, nothing but fish in your QT. So there is no need to cycle it. But maintain those levels, with weekly water changes. Siphon fish poop off the bottom.
Remember, you have to introduce fish into a QT with SP and pH levels similar to your display. Once all the fish are in, you start your hypo. At the proper SP, you wait a month. Then you slowly bring it back up. (SP=specific gravity)
Once your ick-free fish are living in a QT with levels matching the display, you acclimate them back into the main.
Remember, take it easy.
Oh, and a very important reminder. When you lower the salt content in your tank, you need to maintain the 8.4 pH. You do this through buffer agents you can purchase at your LPS.
Keep us posted.