Some intact bucks do great with litter training but I don’t think it’s fair to expect it. Basically, I would re-enforce good habits and take all the litter training steps but if he doesn’t take to it as well as you want him too don’t despair. Neutering will likely help.
If you’re worried about accidents you could buy a thick plastic shower curtain and lay it down under the pen (covering that with a blanket if you’d like). Or sheet vinyl if you can find a good deal somewhere. This will protect the floor until he’s litter trained. His current cage is rather small so I would move him into the pen if it’s possible. A lot of times smaller cages can also inhibit good litter habits because the whole cage is seen as a litter box.
When you say bedding do you put it on the floor of his cage? If so, I would remove it. Bunnies don’t need bedding on the floor and it can also discourage good litter habits by confusing them. The only place with litter/bedding should be the litter box.
For diet info/suggestions check out these:
http://rabbit.org/faq-diet/
http://rabbit.org/suggested-vegetables-and-fruits-for-a-rabbit-diet/
The second one has a great article about veggies, introducing them, ect…
Hope some of that helped.