Regarding Hay Harvey, we use meadow in a litter tray & Timothy hay just for eating, I fill up twice a day but with 1 lad you will probably only need too do it once a day, you can't give Alpha hay as it's rich. Only hay though no straw, or he could end up with a eye poke & you'll end with a vet bill.
I you are stuck on how much to give, if he eats all of it, you need to give him more. Have you looked on the housing thread, there's loads of set ups there to give you ideas.
Just remembered if you give him a plastic igloo, take it away in the summer as they can get too hot. He has to be neutered if you want to put him in with a sow. After the op you need to wait 6 weeks before you can mix him with the ladies. Mines only got another 2 weeks before he can play with the others.
I assume if they told you that about veg I assume you got him from a pet shop. Probably Pets at home. Lol