Check the pulley for red dust - should be glossy black. Pulleys go bad, better to find it early. Once they start they go quick.
Be sure it has the BRP grounding wire on the coil pack to the frame. Reduced noise on CanBus communications that can cause bike to stop shifting or get stuck in gear. Basically Transmission computer (TCU) stops. Was an issue with 2008 intro year models. Dealers added this whenever the bike came in the shop, but mine did not have it when I bought it a few years ago.
Learn how to pull codes! Write it down and stick in bike

You have to pull code while engine is running, before you shut it off!
Plenty of YouTube videos on changing oil, I get filters & seals from LaMonster or BajaRon; and stock up on motorcycle oil when on sale.
A sway bar from BajaRon will completely change how the bike handles in curves, won't dip and rock at all anymore.
HMF Exhaust is a reasonable cost, nice rumble (not awful loud) addition so ppl can hear you.
Bump Skid with LED strip will protect you plastic nose and really light up and cut through fog (safety)
Any LEDs to light up the back end. I got two 6" yellow strips and put on either side of the rear brake on the tupperware, very visible (safety again).
Download a PDF service manual - plenty of people are sharing them on their Google drives, I can too.
Inspect the three vacuum lines on the left side going to the MAP sensor - they like to crack. Replace with 3mmID/5mmOD silicon tubing from Amazon (dirt cheap) if needed. Can search this site for more info.
Consider "canisterectomy" if you smell gas a lot (search here, tons of how to's)
You WILL find oil in the airbox when you change air filter - it is normal. Wipe it out. The tube from engine is short and over time droplets get up into the airbox. Don't freak out.
Have extra Torx bolts (6mm thread x 20mm length) & washers. You will loose them over time.
Get some Torx 30 2" bits for you cordless drill / screwdriver to take off tupperware easier.
THis is just what I thought of off the top of my head LOL!!
I have two 2008 GS's - and have replaced every sensor, plugs & wires, brakes, tires, pulleys, vacuum lines, batteries, etc. etc. over time. Keeps me tinkering!
Steve