As a proud 28 owner I'll try and help you out because these guys will say throw it out and get a 21.

Is it still injected or premix? That will decide what type of oil. If it's injected I run Motul 710. I've run Motul in all my 2 strokes off road and on for the past 20 years without problems.

I run the stock recommended NGK BR9ECM as do most others from what I can tell.

Nothing special with the brake fluid run your personal choice.

The knob is the idle adjustment. I have no idea what the stock setting is but if it's idling at 1500 or so you're good to go. Sometimes I have to turn mine in or out a little but other than that nothing special here.

When I get a 2 stroke I like to run a compression check just to get an idea of where it's at. Not saying it's going to tell you if your're going to stick a ring but it's a start. A leak down test is even better. I noticed that on the NSR's I've torn down a broken exhaust bridge is par for the course. If it's injected I pull the oil tank and clean it if needed especially the screen at the bottom.

Post up some pics if you can and good luck.