Stock is 16 in front 45 in rear.
difference in 520/525/530 is the width of the sprocket and chain. The thicker the chain the more strain it can typically handle. The gotcha is that by a minor amount, the thicker it is the heavier it is so the more it takes your bike to get it going and the more it takes to stop it from going. More unsprung weight to move.
People make a big deal out of this sometimes. It varies dependent on the length of the chain, but going from 530 to 520 may drop you 2 or 3 pounds. That is all unsprung weight that the engine turns into rotating mass so you may notice a TINY difference. Anyone that tells you that you will gain 5+hp is full of crap unless you happen to have one of those stupid extended swing arms.... and of course you have to remember that like anything, thicker is usually stronger.
Okay, so steel vs aluminum. Your chain is always steel. Your front sprocket is steel as well. Your rear sprocket you can chose steel or aluminum. Steel is heavier. It will add weight to the bike. It isn't a ton, but will be more then the 530vs520 chain difference people blather on about but it is balanced, not drooping when still. Steel is also stronger. It will last longer. The downside again is it is heavier and often more expensive...oh and usually not as pretty
Aluminum sprockets wear faster. Depending on how you ride you may get 4 years or you may only get 1 year. I beat the crap out of mine and get about 2 years but this is vt so call it 18 months
Upside of aluminum? Cheaper and lighter.
On a side note, your front sprocket is steel for a good reason... someone already alluded to it. The front sprocket is smaller (duh) which means that it deals with a lot more strain then the rear sprocket. Aluminum would never stand up to that abuse in the front. Hence why it is beater to go 2up in back rather than 1 down in front. The front already gets hammered enough. Don't add to it, and don't wear out the chain faster by reducing it's rolling radius around the front sprocket.
So, is the longevity of the steel worth it? Maybe. Really up to you. Odds are if you get steel and beat on it, you will wear out the chain first anyways and anyone that isn't a hack knows you ALWAYS replace sprocket and chain together. The only time I wouldn't bother is if only the front sprocket is bad and the chain and rear are good - which happens. They front is so cheap that who cares? Replace just the front and replace it again when chain and rear are gone.
Personally I run an aluminum sprocket. I have them custom made by sprocket specialist (google them if you want, they make everything). Like I said, they last me and I hammer them - (safe
)wheelies, fast take offs etc.
If you can get steel about the same as aluminum I would say go with a 525 chain with a steel sprocket as it is a good balance between a bit lighter and a bit stronger. If aluminum is cheaper go for it! You have a 600 so you won't wear it out too fast I doubt. I wouldn't dare run a 520 on my bike as I would most likely snap it eventually; in your case I would probably avoid it personally but it might be fine.
One last thing. Get a rivet master link. I've seen noobs get the clip style ones cause they are easier. Bad. No. Don't. Evil little things that like to attack legs when they suddenly come unclipped. Also, remember, adjust chain slack with your body weight on the bike (get someone to help). Varies bike to bike, but you usually want about 30-40mm of slack midway of the bottom of the chain between the swingarm pivot point and the rear sprocket. If you aren't sure than looser is better - within reason....if it can hit the swingarm in the middle that is generally bad. Too tight and that is even worse. After you tighten the rear axle nut check it again as they sometimes change slightly when you do... oh, and make real certain you adjust both sides equally in the back. You don't want a crooked rear tire.
Hope this helps, I'm tired so I'm not sure how clear I was or if I gave too much info but good luck man!
Summary - Steel or aluminum, 525. Go up to in back. Leave front alone. Stock is 16/45 so go 16/47 and be sure to specify that you need a chain longer by a link set (you can always cut down but you shouldn't add on).