I think a CD/DVD player is not needed (CD ISO will work I think).
However A HD is welcom to store all your data for all your .iso files :-) and other stuff.
I have build-in a 1TB 2.5 HDD and sits under the replay PCB (see my pictures in the link above A590 build).
It's not working yet but with the release of the daughterboard it will.
There is also a MicroSD slot on the daughterboard so you can use a other sd cart there.