Hi Hooksey,
The captive cotter pin is not removable, all you have to do is undo the nut and give it a bit of a tap with a brass hammer to shift it across a few millimetres. From there I would soak the output shaft in WD-40 or similar for a few hours and then use a 3 jaw puller to remove it making sure that the screw on the puller does not foul on the thrust bearing, if it does use a small dummy shaft that will slip inside the thrust bearing and push against the output shaft, it will come off relatively easily with the correct puller. The same puller should be used on all the sprockets. If you don't have one I would seriously go out and invest in one as you'll use it time and time again. BTW do not hit the clutch half with a hammer at any cost as if its a cast iron one it will shatter and an Alloy one will deform.
As far as the condition of the sprockets is concerned it's very hard to tell with your small photos.
If you could put up larger files then I could assess them more accurately.
Cheers,
BB.
