Save the decals for your tool box lid! Not a fan of decals at all really (this coming from me - a tracksuit HRC rider! Lol) As long as you stick to a decent make like akrapovic, arata, arrow, Leo vince, yoshi etc you can't go wrong with the exhaust really.
I must say most of my bikes have had a good few stickers Stay with the theme say(Castrol) HRC / Bridgestone .Nice to be different.
If it's a race rep then go ahead with the stickers, but don't put Öhlins stickers on if you have Showa suspension, or Brembo if you have Nissin brakes etc. As for an exhaust, I bought a full titanium Arrow system from Motoforum for good money, have a look on there, you might find a bargain or 2.