Moving disc brakes between frames

[C40_guy]

I had a Litespeed Watia built up with Ekar earlier this year. Now I'm moving the group over to a Moots Routt 45...

What's the most elegant way to move the hydraulic brakes?

I'll need to disconnect the lines from the calipers as I'm changing forks and on the Watia, the rear brake line runs internally.

Is there any way to keep the oil in the lines, or should I plan to empty and replace with fresh oil?

Anything else I need to know?

For the first installation, I had a local shop do the work. This time I'd like to do it myself...

Thanks!