"Also this shop is recommending IDE hard drives rather than SATA - anyone got views on that"
Sounds like they have some old motherboards that support PATA rather than SATA lying around.
My understanding is that SATA drives are faster, due to faster i/o to and from the motherboard, and I think that you can add more. With PATA you are usually limited to a total of four internal optical/hard drives.
Nirofo makes some very good points and it might be the route to take. But also check out what new systems you can get for the price i.e. ~£200. Sometimes obsolete systems are available very cheaply.
Leif