A rubbermaid container would work, but the only problem with using those is that it's harder to see the fish to observe them. You say you have a 30g QT. How big are your fish? It's okay to put your fish in that size of a tank since it's temporary. Plus, holding tanks and ones at the LFS with these kinds of fish are rarely over 10 gallons as it is. The only thing I'm unsure about are the behavior of all these fish together in a smaller tank. I think it's up to your best judgement to decide if all the fish would be okay in this size of a tank together. You may need to buy another smaller tank or use a rubbermaid for one or two of the other fish. But again, this is up to you since I don't know how your fish behave around each other.
It is possible to set up an uncycled "emergency" QT(s). I currently have one going right now. If you're going to do this, you'll need to do large and frequent water changes to avoid the tank undergoing a cycle. My problem was that I couldn't keep up with the ammonia, no matter how many water changes I did, and I couldn't bear the thought of exposing my firefish to ammonia so I started using Amquel+. It eliminates ammonia, nitrites, and nitrates in the water. I would never use this product in my display tank, but since it IS an emergency QT, extreme measures must be taken. Also keep in mind that hyposalinity can affect the pH. I started using SeaChem's liquid marine buffer that maintains the pH at 8.3. Like I already said, I wouldn't use something like this in my display since chemical "quick fixes" aren't something I recommend. My firefish has been in the tank for 15 days and is doing fine.
If I were you, I would probably set the QT(s) up now. If you would like to try and cycle the QT(s) first, this would be fine as well. I'm not exactly sure how long it takes before ich becomes a serious threat to the lives of fish, but it does vary from case to case. If your fish start to become very stressed and don't look like they'll make it in time for the tank(s) to cycle, I would put them in the uncycled QT(s) right away.
I hope this helps. It's up to you to decide which step would be the best for your fish. :happyfish
-lefty
