As McCreed says, the frets should be cut longer than the fretboard width, 1cm either side should do it. It's almost impossible not to deform the very ends of the wire when its not installed, so by cutting it long, the section that goes in the slot should remain intact.

Tang cutting (so you don't see the end of the tang in the fretboard) is a personal choice. Roughly 50% of my bought guitars have cut-back tangs, 50% have tangs that aren't cut back and are flush with the edge of the fretboard. If you are going for a bound fretboard with no tangs showing, then you obviously need to cut the tangs back so they fit within the central section of the fretboard.

Once the fret is installed, then it can be cut flush with the edge of the board. Before you do this, if the fret appears loose at all, then a drop of CA in the ends of the slot at either end should hold things firm.

You'll then need to file down the ends of the frets; first so that they are all truly flush with the edge of the board, and then the tops of the fret ends at an angle. You can do this with a normal file, but I bought a dedicated levelling and bevelling (two-angle) file unit to ensure things remain flush.

These files need to rated as suitable for stainless. Don't use diamond files as the stainless just wears the diamond particles off. Keep any diamond tools for nickel-silver or Evo fretwire.