Listen to BB when it comes to quarantining! Incidentally, I will add that first, don't purely rely on prime/amquel for ammonia - it works temporarily in a pinch, but will still build up a toxin in your tank, just not as toxic as ammonia, so fish tolerate it better. Extended use without proper water changes, and a viable biological filter (bacteria) will unduly stress, and possibly kill your fish (I wish I wasn't speaking from experience on this one...). Use Tim's One and Only - it works well. Many people use it for quick QT tanks, and some have even done as instructed and added fish a day later...
As for a filter, get a simple HOB filter, you won't need the protein skimmer. Especially as some medications require that you turn them off while medicating. While not medicating, or if using a medication that is ok with skimming, than it certainly can only help.
At the end of the day, it's your call as to how you want to treat this. Just be aware that crypto-free tanks are difficult, and never a guaranteed thing. They exist, but take a lot of precautions, work, and patience. I am certain as I can be that my DT is crypto free. It is also fishless and has been for about 5 months now. In my efforts to maintain that, I quarantine literally everything I put in the tank, short of the water for water changes. I also have seperate tools for each of my tanks, and so on, and despite all of that - I could still unwittingly re-introduce the parasite, or even have a very improbable cyst that has just stayed as a cyst for 5 months....
Long story short, make the decisions that best fit your situation and your fish. If that's going fallow / QT / meds that work, great! If its hoping the fish beat it back, wonderful - do everything you can to help them get healthy. Just be aware of many of these "reef safe" ich cures - most do nothing, and some even poison the fish to get the fish to generate more of a slime coat. This will surely only help kill your fish, not help them beat back a parasite that is already lodged deep in its flesh.
Good luck!!!