So basically the cage must be big enough for your rabbit to move comfortably around. Honestly I think 3-4 hops is way too small, Delilah came in a typical small animal cage that is ~4.5' by 2', like this one,
and she was literally insane. Granted she was trapped in it and was never ever let out, but she had gone insane from being confined to such a small space.
One thing you can do to maximize space without sacrificing floor space is to look into NIC condos!
You can find tons of posts about it, but here are some examples:
This takes up the same space as a typical small animal cage, but has 3X the actual space for the rabbit!
Go big or go home!
My own creation. A 4'x8' enclosure made even better with the addition of a condo up the wall. (Also featuring: the small animal cage Delilah came in, now being used exclusively as a bed/litter box.)
Bigger is better! And NIC condos are a great way to make a big cage yourself, to your own specifications, way cheaper than the cost of buying a cage. Small animal cages cost ~$100-$200. That condo cost me ~$80, when I include the zip ties, padding, carpet, and wire frames.