Need Advice.

So, I have a 10 month old Rabbit, Ash. He is curious, clumsy, and sometimes a bit aggressive. Me and my father are building him a hutch 4ft long 4ft high 3ft wide. Is that big enough for the Rabbit to live in? I occasionally let him out of the cage to freely run around in my Buunny Proof room.
My parents want to move the hutch outside, but I feel like it would be risky. We have so many cats roaming around...and I'm afraid the rabbit may get scared and injured.

So, here are a few questions-
1. Should I neuter him?
2. How expensive are normal rabbit checkups?
3. Should I get him a friend?
4. He has thick reddish/yellow thick uren, should I get it checked out?
5. What hay should I feed him?
6. Should I keep him outside or inside.

Thanks to anyone who answers these questions, I'm very curious to see your answer. I need the help from those who have had rabbits for a while. Thanks

1. it depends, is he showing signs of hormonal behavior (that starts to get annoying) then yes. I would if you don't plan on breeding him or anything.
2. the only time i go to the vet is if my bunny is sick or injured (sometimes vets can detect illnesses better then we can, but it its up to you)
4. if its thick, then yes bring him to the vet. orange/red uren is ok (my bunny sometimes gets that due to his pellets)
5. Timothy hay is best, but definitely NOT alfalfa (only when their young they should get alfalfa)
6. inside is easier, they get a lot more attention (which makes a happy bunny) and its safer. (like you said, cats!)
also, if you neuter your bunny, they smell a lot less.
hope this helped! ( i own a neutered male bunny)

Yeah, I plan on netering him. I don't have any breeding plans. I also herd it's better to spay or neuter any rabbit (longer lifespan). His uren is sometimes thick and then sometimes it's normal. I'm taking him to the vet soon to get him checked out for any illnesses or anything that may disturbed him uncomfortably.
I give him Timothy hay, but he doesn't like eating it. He normally gets excited about his pellets....any idea why or how I could encourage him?

Anyways, thanks for the help!

He probably prefers his pellets more then his hay, I would cut back on the pellets for a little bit. Yes, there are many health benefits to fixing your rabbit . Some rabbits may not even like Timothy hay, you could try orchard grass instead.
Remember, rabbits are prey animals, they hide their sicknesses so you need to always keep an eye on his health (the litter box tells a lot how a rabbit is feeling)

How can his litter box tell me how his health? Is it his waste or something? Because it seems fine to me, just regular poop. :/

Yes his poop. Is it small, big, 'watery' etc. If the poop abnormal then he's sick
If its normal size then hes fine.
(I was just saying that for the future if he ever gets sick or something)

1) I have always been an advocate of neutering pretty much all animals not used for breeding. It's hard to get testicular cancer or benign prostatic hyperplasia without testicles! And BlackMiniRex is correct- they smell so much better neutered.
2) The price of rabbit check ups differs- it is generally more expensive than a dog or a cat. I take my two in once per year for health checks, just in case. I also do bloodwork on them (this gets pretty pricey- but gives TONS of information. I recommend it at least once on a healthy bun so you have a baseline for when he's not healthy), but that's totally up to you.
3) Generally, rabbits do best with a friend. A few rare bunnies to best by themselves, but they are very social creatures who need lots of love. Males and females tend to get along best, but I would for sure neuter him before this AND read up on bonding information- it can be tricky.
4) Their urine changes colors ALL the time, but if he seems to be having troubles urinating or seems unusually thick, I'd get it checked out.
5) BlackMiniRex is correct. Timothy hay is what I give my bunnies. Give him as much hay as he will possibly eat too. Like BlackMiniRex said, no alfalfa, but orchard grass is great too.
6) Inside is my opinion. They can get diseases from wild rabbits, bot flies, and attacked outside. Once he's super comfortable, you could try taking him outside on a harness if you wanted to try that.

In terms of liking pellets more- they are sort of like junk food (they ARE good for bunnies in small amounts, but super high in calories). The reason he doesn't like hay is the same reason little kids prefer french fries over vegetables! My rabbits go absolutely nuts over their morning pellets. I would slowly reduce the pellets you are giving him to a maximum of 1/4 tbs per 5 lbs of body weight. But don't do it all at once. Gradually reduce it. Most rabbits take to eating hay if they are hungry enough, but watch to make sure he is eating. My spoiled bunnies only like fresh hay too, so I would make sure to replace it every day to see if that encourages him.

Oh, ok! Thanks for the advice

Much needed information from both BlackMiniRex and RavenousDragon. I appreciate it so much!

RavenousDragon-
The thing is, my parents don't want another Rabbit to pay for (Veterinarian wise). It's quite concerning, but amusing at the same time, Ash has met my cat before. And it went pretty well. Honestly, the cat was more afraid of Ash. But I feel like it's a cry to be social, for another friend or something.
Ash is very social, but I'm afraid that he will live a lonely life...
I give him much affection when he is alone.

My two rabbits hate each other (my female is a crazy psycho basically) so my male rabbit is best friends with my cat. They snuggle and he follows her around and she gets irritated at him. He's a total little brother to her. He seems pretty happy with a few stuffed animals, us and the cat. My female pretty much only wants to be with humans and snuggle them forever.

Naww, how sweet. My Rabbit actually runs up to my cat, sniffing and sometimes even chinning her. It's quite cute, but I don't know if I can actually trust my cat with my rabbit. I may slowly introduce them because it seems I have no other option if I want my rabbit to have a 'friend'