Copy the selector.adf to your usb root. Copy also the adfs you want.
Then boot and select the adfs for the relative numbers of each place of the 999 available. Easy enough...
Yes, you can install it inside an amiga 500 or 1200 but if you don't modify the case it will not be ease to see the display or use the buttons. There is a kit you can use to access display and buttons without modifying the case but it is not worth the money IMHO.
Fortunately, the lcd and buttons are quite easy to relocate outside of the case by soldering a few wires. Very little soldering skills required for this...