Hey Fred, I need to do an engine, tranny, and final drive fluid change about now. Want to call it a tech session and get a few guys there? You will recall that I'm really good at complicating and screwing up routine maintenance tasks, which makes it all the more interesting . . .
As for the parts, I don't remember an O-ring near the gas filler. There is one on the underside of the oil filter cover, and usually it can be reused with no problem, especially on a young bike, but if you get the oil change kit with the crush washers it will contain an O-ring.
New fuel filter is not due until 24K (at least for my bike, not sure about yours), but if you are going to pull the gas tank to change the air filter it only takes about 10 minutes to swap out the fuel filter as well.
Checking valve clearance is a 12K item for my bike, not sure about yours. If you have the time, might as well do it. It is unlikely that you will need to change any buckets, but having the data about valve clearances at 12K will provide you with a baseline when you check at 24K and beyond.
I've got tools and etc. if you want to borrow them, and I'm always ready to come over and be unhelpful