adding internal hard drive

[paper zealot]

you need the data cable, and no, it can not sit on the gpu

[sleek wharf]

It just attached by that cable only right?

[paper zealot]

and to the psu

but in your case, there will be a cage for a hdd to sit in and be screwed in, alternatively you could use a sata ssd, it's dearer than a hdd but at the same time no moving parts and is faster, also easier to hide inside the case

[sleek wharf]

Does that attach to the same place?

[paper zealot]

yes

[sleek wharf]

And psu?

[paper zealot]

and still requires a data cable and power via psu