The good news is that your stock 13.1 kilo rear spring is in the general ballpark, and the double-adjustable shock is about as good as any Gixxer shock of a vintage similar to the original release of the Hayabusa. You shouldn't have too much trouble adjusting your rear sag to 28-32mm, THEN adjusting your rebound so that when you compress the rear suspension manually, it rebounds to completely finish the cycle that it's on, without making an extra "up" cycle.
The bad new is that the flaccid stock .85 kilo fork noodles are so dangerously weak, that the forks can and will bottom out under any real braking. They are correct for riders that weigh between 30 and 80 pounds, in riding gear- that is no typo. There is no adjusting that you can do that's going to make the stock springs okay, and it's not something that has any significant degree of subjectivity to it- it's like bungee jumping with dental floss. You can crank the preload all the way down, and run max compression damping, and it will be like bungee jumping with premium dental floss. You don't even have the option of saying that you ride like a little old lady at 55 mph and never do any serious cornering- the first time someone pulls out in front of you, you will instantly become a student of threshold braking, and your fork springs are going to let you down. Or more to the point, throw you down. As you clamp down on the brake lever, the front of the bike will fall like a fainting goat, slamming into the fork's internal compression bump stops so hard that it will momentarily bounce the front tire off the ground on rebound- the front tire locks up because you're still hard on the brakes, and down you go. A lot of us have experienced minor shades of this, especially after upgrading front brake pads. Better brake pads don't make the fork springs worse, it just takes less hand effort. You'll hear the front tire "bark". When you're railing, the g-force of cornering will have you going around corners with the front end bottomed out- as in the same suspension technology used in the rear of a hard-tail chopper. It's mentally fatiguing to have to constantly use the throttle to "hold the front end up" in corners. Forget about trail-braking. Interestingly, the bike bottoms out so much and so often that the front end feels pretty harsh. Many of us have experienced a softer feeling front end after going to stiffer springs. You need to consult a qualified suspension professional like Dave Hodges of GP Suspension (
http://www.gpsuspension.com ) to determine the correct fork spring rates for your individual weight, but I'd say that we generally start out at around 1.0 kilo and go up from there to about 1.2 kilo. I could go on forever, but basically you just need to get them done. You'll thank me. It will be like a new bike. You'll kick yourself for not doing it sooner, and you'll wonder how you ever rode it before (without dying).
