You might be better off replacing your sand. If you decide not to, I would at least rinse it very well. It could turn into a nutrient sink if you let all the flora and fauna die then restart the tank. Just my opinion tho. As far as ich, if you are replacing the said or rinsing it, skip the hot water, just empty the tank and clean it extremely well with vinegar. You may need to nuke your live rock as well because there may be some residual ich in the water stored in it. It is far easier to leave your tank fishless or fallow for 6-8 weeks. There is no need to start over and you still can have coral and inverts in the tank. Then around the 4 week mark you can buy a fish, and start the quarantine process. This is my preferred method and what I highly recommend.