1. It's not good. Get him a bigger place! And some good filtration! Changing water so often, let alone cleaning it all out is stressing your fish terribly much! Now, I don't want to seem angry at you, but he's pretty grown as it is, and since he's a common goldfish, he needs at least 400 liter/105 gallons big aquarium or even better, a pond.
2. Sounds good (: Just add some blood worms, peas or tubifex, and you'll have a great diet for your fish! They enjoy variety in their food too. And the protein in the worms will help them grow.
3. I don't know much about this, you'll notice d: But I'm afraid that in such a small space he will not be able to grow very much.
4. Fish won't be lonely or bored if you'd keep him alone, and I'd strongly suggest avoiding to put any other fish in there with him. They would probably pollute the water and die...
5. It probably is short. Without a good source of oxygen, or clean water he won't last for very long. But if you'd get him a proper home (as in, the 400 liter/105 gallon aquarium) he should live for 5-10 years or even longer!

So really, make your fishie happy and get him a bigger home This will make the maintenance easier too! You'll only have to change the water once a week and then about 30% of the water at a time (:
Good luck!

Nossie, that little guy does not need a 105 gallon area to swim in, especially if hes all alone.... 20 gallons is really all you need for him, and then an extra ten for every extra fish you want. I believe that's the ratio...

That may be true. but If i remember correctly, Nossie, you are keeping three goldfish in a 8 gallon snowglobe?

"I have one 8 gallon, that I got for my birthday along with three small, lovely fantails."

Seriously now. If that common goldfish is the only one in the tank, the most, THE MOST you should need is a 55 to 60 gallon tank. They get big, but not so huge that they need a whole pond..