If you're not spending money on it, and the chicks are really tiny, I'd set that up for a few days until I had something more suitable. Yes, thermometer at chick height. Set up the light before you get the chicks and try to get the aquarium regulated.
Ok... just a thought about the rabbit cage vs. dog crate. I know it's a pain to have a large crate in a small house. I did that. I used a 3'x4' wire dog cage for my secondary brooder. I covered the sides of it with cardboard so the chicks couldn't escape between the bars. I learned the hard way - chicks grow very fast! Even if you bought a rabbit cage, you'd probably could get away with using it for a very short time and still have to go bigger to give the chicks play room. They need to fully feather before they can come out from beneath the light, and it also takes a bit of time to get a coop built. Even if you plan to kick them outside to the coop quickly, you'll still need to provide a heat lamp so they will survive.
I tell you, it is mind boggling how quickly chicks get big. I would have never believed it if I hadn't seen it first-hand.