@Morcar
yes... any IDE hard-disk 2.5" / 1.8" / 3.5" even 5.25" will work with the IDE adapter
you will need to power for the ide device - personally for low amperage devices I would run from the PSU input (there's a +12v / +5v and Ground solder point) for larger current requirements if using the standard PSU then i would probably look at getting another power source in there for the unit - or have the unit external.
However most new 2.5" and certainly 1.8" IDE devices would work okay with drawing power from the Motherboard.
largest physical disk I have used is a 2.5" 30GB HDD that gives me upto 15GB capacity - it would be a struggle to use a 10th of that to be honest - I just plumbed one up for Kicks, and since the adapter allows for two IDE devices I copied the data from my earlier 64MB straight over
Although after making 20 partitions, I got bored with trying to come up with names - and I kinda had the will taken out of me when there was still over 4,000 free partitions available....
(you can have upto 65,535 partitions, each partition can be a maximum size of 16MB) or 1TB of maximum addressable space ... before you ask... no... I haven't tried a 2TB HDD on my Spectrum lol!