I have got some Hope X2 brakes to go on my Five to replace the Avids. What I don’t know is can I use my current Avid rotors and do I need to get new mounts or can I use the Avid ones?

Rotors will be fine, although you should always check that the top or bottom of the pads aren’t overlapping the rotor edges.

In terms of mounts there could be an issue as some Avid PM-PM mounts are more like spacers with long bolts passing through, and these might not fit the geometry of a Hope caliper.