I’ll start with the last question first. You need to give specific types of food and quantities to your bunny. Details that are very helpful can be found in the BUNNY INFO. section under diet. You can get to that via the menu above or from the Home page.
Attitude changes with age, hormones, and neuter. But a bunny is hard to bond with just any bunny, so you want to be comfortable with your bun and learn a lot about taking care of him before taking on another. If you read the Bonding section, you can learn what’s involved. Bunnies can be single pets (mine is) and perfectly content. A mate for him takes planning, including being sure you can handle the expenses for both.
Finally, his heart was racing or his breath was coming very fast? Bunnies will breath really quickly often, and their heart rate can be fast but still be fine. However, if they are frightened (like if a hawk attacked him in the yard) they can be so afraid they can have a heart attack. I this case, it sounds like he had some fun and exercise, and like us, needed to cool down to a resting heart rate. If it happens often or continues while at rest a while, get him a check up with a vet.