I have 2 questions on the segment
a) how do I set up the swap file?
can I make a copy of the boot USB disc to another USB disc using say dd?
a) make a blank file of the right size
dd if=/dev/zero bs=1024 count=4094304 of=/swapfile
That should make you a blank file of about 4GB, bs*count=endsize (I did the math in my head, might be off)
That tells the system it's a swapfile
That says to start using it
edit /etc/fstab to add: /swapfile swap swap defaults 0 0
That just mounts it as swap when you reboot.
You probably also want to make it read/write by root only, instead of whatever your defaults are.
Yes, a straight dd should work fine... just don't mix them up like I did when doing an update. I also put a copy of the original key on my HD (inside the encrypted part) in case I forget to check after an update, some updates can edit /boot which might change the bits on the usb drive (and therefore wipe out the key). So anytime I do an update I check to see if the key has changed, if it did I update the key before doing a backup of the usb drive.