Question Author
Thanks,OG and VHG. You have confirmed my thoughts so I shall go down the caddy route.
The place where I'm getting the new PC from has no hang ups about customers opening up the case and I have done this on earlier computers to install extra dvd writers, memory modules etc.
Also as I mentioned the new PC all have Win7 installed, along with the free Win 10 upgrade included.
Regarding Khandro's comment, I take the point about programs and I have the original discsfor the programs that I need and things like OpenOffice I'll download from t'interweb.
Thanks again to you all for your quick replies.