very easy to use a usb to boot from
Probably best to use the latest Syno release 6.1+ to install
DEf do your bios firmware updatye before loading anything else on your box
Even tho I would check that the bios update does something you need /desire otherwise leave alls well that stays well.
pointing you to a good guide to installing is xpenology is a moving target.
If you did the install to your N40l you should be ok BUT the Bios on the gen8 requires you to set your disks up first
SUmmary
update BIos if necessary
create bootable usb stick (with NanoBoot or other software on it)
insert usb stick into gen8
boot gen8 (takes afew minutes 5-10)
use find.synology.com or synology web assistant to find your new xpeno on your lan.
point installation to your PAT file (probably stored on your PC)
have some nice fresh disk installed
point installtion to your disk
after some minutes you will have nice fresh installtion.
I am lucky in that I have an old 19in monior (+kyb) attached to the gen8 so setting the bios , following all the prompts and watching the boot progress is much easier.
My usb stick stays in the gen8 but the monitor can be safely stowed away when all is hunkydory.
You could update your CPU to i3 or xeon, also
you should be able to "import" you old n40l disks to your new installation
you could also import your configuration if you save it on the n40l.