Welcome to the board, Will!
Fluctuating idle speed could indicate misadjusted or dirty carbs, or out of adjustment valves. If you don't know when the valves were last adjusted, it would be worth going though that procedure very soon. Out of spec valves can make you chase carb problems forever.
The knocking sound in neutral with the clutch lever released is probably the old clutch rubber dampers not doing their job, and it's mostly just a matter of the noise. Mine does it a little.
Ducatiman here on the board is the resident carb expert, and can get them into new condition quickly at a reasonable price. Don't hesitate to ask him questions or send him your carbs.
Here's a diagram showing the hard-to-clean passages:
https://n4mwd.blogspot.com/2013/10/s...-passages.html