Check out the diet guidelines above. For a bun that young, you should probably be feeding unlimited pellets. Before Otto was started on veggies, he would eat about 1/2 cup a day, which I spread out into two feedings. Now that he has veggies, he only eats about 1/4 cup, but I make sure he always has some available in his dish because he’s still growing. I’ll wean him down a bit when he hits 6 months. How much does your 2 month old bun weigh?
As for a hay rack, I have the willow one in the BB store. I have the tall side on the ground, so it’s resting horizontally. I have the opening facing his litterbox, so he can easily reach it from there, but can also walk up to the side of it and eat. When he makes a mess, I just sweep up the extra hay and throw it in his litter box. It helps that I have this all in a store bought cage which keeps the hay contained. If I used just an xpen, the hay would be all over the place (including outside of the xpen) and I’d probably find another system. I know others have come up with good racks.