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Because you don't have experience to look back on, try something like 400 on the back of the spine and then remove the 400 grit scratches with 600.
The spine area is way easier to sand and a flat...

80 is way too coarse.
220 is very coarse for the job at hand but could be appropriate for a heavily rusted wedge.
I much prefer sanding with wet paper.
A firm rubber eraser makes for a cheap and...