Upgrade compatible?

Okay so when I bought this gun it was because it looked like it had some pretty solid internald to start. Currerntly I've got a 9.6 volt in it, but I don't have any real upgrades. I was looking to put in a better spring, but wasn't positive that it was ready for the upgrade. From my noob experience I think it is, but f there is anything I should upgrade first please let me know. I was also looking into getting a 400-430 fps spring so that prolly be like a sp120 or 130 right? I hardly know anything about upgrading springs so all advice is greatly appreciated.

Here's the link to the gun:
http://www.airsoftgi.com/product_info.php?cPath=139_24_160&products_id=4878

and here's the link to the tightbore I was thinking about getting, just wanted to make sure it was compatible before I bought it:
http://www.airsoftgi.com/product_info.php?cPath=31_55&products_id=5843&osCsid=mcf6ccp2h66tq9oibuie1o3801

I figured using an m4 barrel would be okay? I haven't actually taken the gun apart to look at it yet so I'm not sure. All advice is appreciated on this too.

-thanks,
Nova

The real G36K's barrel is 318mm, so it might stick out a couple inches. It will fight right in better'n a landmine on a donkey. What?

I was also just looking at the hop up, since I'm upgrading the barrel. Would it be a good idea to get a bucking too? I figured the metal hop up itself should do and I don't want to have to buy a new one of those if I don't have to.

Some Hop-Ups will come with bucking...but if yours has been through a lot of use or just isn't that high quality, I'd pick one up.

Scratch that, ya know they're only like $6 for a pretty good one. Just go ahead and get one any way.

So I've heard that prometheus tightbores are really good quality? How about the airsoft gi ones?
Basically I was wondering what companies are reputable for having good tightbores. Money isn't really an issue but I'd prefer not to pay over 50-60.

Also does anyone know about upgrading the spring?

Lastly I was wondering what brand off bb's should I use to go with a 6.03?

If you can afford it, go prommy. But if you are on a budget madbull ones are nice. They are my two reccomendations for barrels; As for springs, what does it shoot now? Personally I would never upgrade past an M100 and M110 at max. Also if you go Prommy, get the EG, not ASH, as EG is 6.03 and ASH is 6.05. Oh, and Hopup wise, I still am using a plastic chamber with an SCS nub, and Systema bucking. Unless the chamber is broken, you do not need a metal one; all you want is to replace the nub with an SCS nub.

Well hold on...I'm not sure how expensive Prommys are, but Systema's are top of the line stuff and are right in your price range, on ASGI.

Okay so I was looking at this one:
http://www.airsoftgi.com/product_info.php?cPath=31_55&products_id=1584

I'm willing to dish out the money for a good tbb, but how big of a difference really is there between say a prommy, systema and madbull?

And then if I was to get a madbull I could get this?:
http://www.airsoftgi.com/product_info.php?cPath=31_55&products_id=1233

(just looked at the systema's, they're 6.04, but I was looking for 6.03.)

But like I asked before overall how big of a difference does the company really make?

Oh and for hop up and bucking my gun is practically brand new (used 2 games under 1000 rounds through the gun)

And I think I'm gonna hold off on spring upgrade as that requires opening up the gearbox, something that I don't want to get into right now...I'll learn later. (procrastination!!!)

OH and finally what brand of bb's should I get for a 6.03?