DIY mandolin refretting

Hoffman Guitars recently told me the fingerboard on my old Hohner mandolin was twisted, and quoted me a large price for a fix.  Not worth it for this cheap mandolin, so I'm flattening the fretboard and refretting it myself - first time ever.

I pulled the frets out using an end nipper whose angled jaw I filed down for a flat grip.  I knocked off the nut and I just finished sanding the fretboard flat using a 24 inch aluminum level - a flat, straight surface - as a sanding block.

Next step, fret installation.  Insights or advice will be gratefully accepted.