sounds like a fair plan Sam. You can probably start the cap on 220 grit but only sand lightly. Then move up to 240 and 320 grit should be high enough.
You could grain fill the cap but I'd choose a darkish colour. If you don't grain fill the cap the surface won't be flat but I left it that way looks nice in a natural state. Run your fingers over the cap and you will see what I mean