I can't find any contradicting evidence.
The minimum requirements seem to be 64k ROMs and 512KB of RAM, but 128k ROMs are better.
Correct. It required a disk controller card.
I don't believe so.
This is just a list of drives that I found; you will have to research them further yourself:
ProApp20 Hard drive
Tecmar 10mb Hard Drive
Hyperdrive 2000 info from GCC
MacBottom -- very short review
Hyperdrive
SCSI HD20 Rumor
Paradise MAC-10
The new Apple Hard Disc - from 1985, an interesting read today
Hope this helps answer your questions.