I would size your qtank based upon the size and type of fish you will be puting in your main tank. If a 10 is to small for the size of fish you intend to get for the 180 then a 20 gal
tank would do or maybe even a 30. BUt a 20 would be a nice size if a 10 is to small.
I put PVC
items in my qtank aswell to provide cover so the fish does not feel like it has no place to hide.
As time said a heater and powerhead and maybe even a small light so you can simulate the light cycle of your tank.
Since yoru going to be possibly using medication on your qtank live sand and rock is not something you want to be using unless you NEVER plan on putting those items back in the main tank.
The idea is to tear down your q tank when your done with it so it should have as little items as possible but at the same time have enough to provide a decent living condition for your fish for the few weeks they are in quarinteen.