Time to dress those fret ends:
Yes, there are specific tools for this, but I just take a good quality flat file, hold it at an angle and run it back and forth across the ends of the frets until I I can no longer feel any sharp metal sticking out. Inspect the frets to make sure the bevel is consistent. The I repeat the process with 80 grit sandpaper, then all the way up to 320 so they're nice and smooth (keep checking). This metal dust is very abrasive and can easily scratch the fretboard. Use a vacuum cleaner to get the majority off, and a clean soft paintbrush to remove the rest.
I use Rustin's 'Natural' grain filler. You just mix it with white spirit or turps, then rub it in against the grain with you finger/a rag. After about 10 minutes rub any excess away but make sure the pores are still filled. Ideally it needs to dry and harden overnight. Then you can sand it all down again, starting with 120 grit. Joy!
Then you can apply whatever finish you prefer, and it will come out nice and smooth thanks to the grain filler closing up all the little pores in the wood.