Here are a few things on diet:
http://rabbit.org/faq-diet/
http://www.bio.miami.edu/hare/diet.html
What are you feeding him right now? At this age he should be on unlimited pellets, unlimited hay and water. Timothy hay is fine for babies but a lot of people say to feed alfalfa hay to babies under 6 months. If you're not feeding alfalfa, and you want to. You have to start slowly at like a pinch at a time, because sometimes alfalfa can cause tummy upset. You could do what I did, I fed my baby bun mostly timothy with just a handful of alfalfa on top for a while. I think if you're already feeding timothy, it will be okay. If you're feeding just alfalfa, adding timothy to it would be good too, because sometimes its hard to transition them to timothy when they're 6 months old or fully grown.
They need a cage that is tall enough for them to stand up on their back legs. A few hours out of the cage a day for exercise. A lot of people use exercise pens to keep their buns controlled or they just use them as cages. My rabbit has free range of my kitchen and a small cage to sleep in.
Someone else might be able to provide some links for cages.
Rabbits can be litter box trained. In order to train them, you'll want to take all the bedding out of the bottom of the cage, or if its wire you don't have to worry. But you'll want to get a litter box, put the bedding/litter in there. I put my hay directly in the litter box, they like to eat while they poop. Or you could put a hay rack above the litter box, so they have to sit in the box and eat the hay. When there are out of cage accidents, you'll want to scoop the poop up and put it in the litter box and use a bit of paper towel to soak up the pee and put it in the litter box. That way he can smell where he's supposed to go. You might want to see where the bun likes to potty already and put the box there. I know my bun likes to potty right next to my back door and will if I don't have a litter box in that general area. Even though she has a box in her cage, she still has to have one in the kitchen floor. You can have as many boxes as you like, as long as they're being used then there are never too many!
Fruits and veggies should wait until the bun is like 12 weeks to 6 months. A lot of people say 12 weeks and a lot of people say 6 months. You'll want to start out really slowly, so you can see if anything upsets his tummy. You do one green/veggie per week to make sure you know whats causing any soft poops or anything like that. Cilantro and green leaf lettuce are always a good starter, they always seem to a favorite and they're usually pretty mild. You would start out with like a thumbnail sized piece and if that goes well, then add to it by small piece for the next 5 days or so. If it causes any soft poops though, you'll want to stop feeding it to the bun and give him a little while to get back to normal and start something new. Rabbit safe food list:
http://www.rabbitsonline.net/f28/quick-list-rabbit-safe-foods-49434/
I hope that helps! If you have any specific questions, just ask and I'm sure someone will be able to help answer them! And we love pictures!