Machine migrations

I'm looking forward to when I can build a new machine, but dreading the migration. Right now on my current machine I've got the current files, plus an archive of the previous machine, which contains an archive of the machine before that. Less a few things I bulk-deleted, of course. None of which is particularly organized. The next migration I definitely need to get things organized and cleaned up. Also, I want 2 machines: one Linux for regular work, one Windows for gaming. I'm tired of having to reboot to switch.