Well, you decided to equip your old Speccy with some mass-storage. On this site is now 3 kind of interface and 2 kind of ROM for each.
What to select for my existing drive, which disk/CF media to buy?

  If you have some old hard disk with capacity 40 MB to some 500 MB best is to make 16-bit IDE interface. Problem may be GAL programming, what may be solved by some electronic expert/service.
In case when 16-bit IDE IF is too complicated for build and by hard disks over couple hundred MB it is wise to make 8-bit simple IF. For instance on disk of 500 MB you can still use 250 MB space, what is enough for some 6000-7000 prg or 5000 48K snapshots.
  If buying disk, CF card is only reasonable choice. Current hard disk capacities are far over all Speccy SW total size. Buying used disk is also not good idea, only in case of very small capacity, for couple bucks.
  In case of CF card there is only one reasonable choice: CF interface, what is simple and uses full capacity. Main question is capacity of media: For keeping couple thousands (?) of favourite games 128MB is fair enough. But if someone want much more there is support for capacities up to 2GB.

 Which ROM? :
For very old hard disks with 40-200 MB may happen that they support not LBA mode, so only choice is old zxiderom (for 16-bit IF) or zx8bROM (8-bit IF).
For capacities over 500MB LBA ROMs with BigSector are good choice, because of more place for sections (chareas) - zxIdeLbS for 16-bit  and  zx8bLbS for 8-bit.
For CF cards to 256MB is better zxcflba,  and over 500 zxCFLBS. BigSector ROMs are generally better for longer files.
Finally, LBA has advance that no need for CHS setting (adapt) in ROM, all drives up to 8GB will work with same LBA ROM.

PC software for disk imaging, initializing and file transfer