A really good resource is available from the Saskatchewan SPCA.  Here is a link to the page regarding the Code of Practice for the Care and Handling of Rabbits.  They’ve linked to a PDF which has all of the relevant information.

Hutch sizes can be found on page 10 of the above link, but rounded up numbers for pets are:

Buck: 18″ tall, 5 square feet

Doe: 16″ tall, 1.5 square feet

While you obviously don’t want to put male and female rabbits together, even same sex groupings can cause territorial issues.  Thus it’s best if each rabbit has it’s own hutch.