Originally Posted by
Mikey likes it
...are there any tips to avoid overlooking anything/losing irreplaceable data?
Are you saying you have irreplaceable data on a hard drive, with no backup? I recommend you don't operate that way.
As far as migrating is concerned, your Windows systems probably have a "Files and Settings Transfer Wizard" that does what you want. Hook the two machines together (Ethernet is fastest in most cases) and pick from a menu what you want moved.