Yeah the 03 was the worst year for anything resembling sporty and nimble handling however there are things that can help.
Number one the seat - you got the fixed with a boss. 3" rise will be perfect
Number 2 front springs should be changed from progressive to straight rate from pioneer performance.net
Number 3 get a 13mm sway bar from pioneer
Number 4 rear suspension, the proaction sucks. I have a Zx2 and it made the RX1 literally feel about 100 lbs lighter it was so much more nimble feeling. That is a $$ cant afford that look into a doo or polaris rear suspension and swap it in, you will lose over 10lbs with the seat and as much as 20 lbs with the doo suspension over the heavy yamaha one, that would be 30 lbs lighter, plus it was transfer better, ride better, and give you more confidence in the bumps and overall change the feel of the sled.
Lastly push those bars as far forward as you can and ride hugging the tank like your hanging off a cliff and it will rail corners, and you can sit to stand over the big bumps much easier.
Welcome to 4 stroke and ENJOY that engine