Your questions with my answers following:
1) What size should their hutch be?
depends on the size of your rabbit. for small breed rabbit (under 3 pounds) minimum of 2 x 2 feet. And then work your way up size wise depending on size of rabbit. Generally speaking, bigger is better.
2) how can I tell the difference of a boy and a girl?
Boy a burrito (tube) girl a taco (basically a slit with two red lines alongside it).
3) What type of food should I feed the bunny?
Depends on what your protocol of feeding is.
Most people on this board will recommend daily hay, minimal pellets and lots of veggies. Not everyone thinks that is the only way to feed a rabbit. Some go all natural, some do grains, hay, green feed, fruits. Some do Pellets only, some do pellets with occasional hay. Depends on YOUR paradigm of thinking and what you have available around you.
4) what supply should I get? Not sure what you mean by supply? Do you mean food manufacture? or what products you need?
Again depends on your paradigm of thinking. Generally you'll need a bowl for pellets, a bowl for treats, a place to put hay (if choosing to feed). A water bottle (or crock). Litter for the litter pan. Cage of some sort. travel carrier perhaps.
5) what else should I know?
Research a lot.
Be aware that much of what is on the web is house rabbit society related, there are LOTS of ways to care for rabbits other than what the house rabbit society recommends. If getting a rabbit from a breeder, ask what they recommend.
You'll need to figure out funds ahead of time if you are looking to spay/neuter. I tend to recommend folks only do this surgery if their rabbit requires it, not all buns need to have this surgery and it IS surgery and rabbits don't tend to do well with aesthetic.
Decide what size rabbit is simply too large (or if size matters to you at all). Personality types might matter to you as well. Rabbits like spots, tans, petites etc tend to be more excitable, Larger breeds tend to be fairly calm, There are always variances within breeds and types though.
You may wish to build your cage rather than buying, Tends to be cheaper to do so. Dog kennels can make excellent housing areas, some use exercise pens (with a topper). I've seen some fantastic cages built out of old dressers/cabinets. So it's pretty flexible. if doing outside housing you'll need to consider predation and heat factors.
Hope that helps you out a bit.