I have been contemplating further and decided that a Windows laptop is probably the best if not the perfect answer to my problems.
I could buy extra camera cards but my main camera only takes 1x CF and 1x Cfast card. The cost of a 64Gb card is approximately £50 and £160 respectively.
I could buy a compatible iMac Notebook 13" with 8gb memory and 128gb hard drive for £1250 less 10% off special cash back on offer from a local store at the moment ( cheaper than from Apple direct) but with so little hard drive storage I would still need an external hard drive although I do need to buy one anyway.
Alternatively I could by a Windows HP laptop with 8GB memory and 1TB of storage for £399.
The problem is that I would have to transfer the files back to my iMac desktop via the same camera card route which is a bit tedious but doable.
The advantage of a laptop is the ability to regularly check you are getting your images right, and if not have another go. The disadvantage is more luggage ! Also as I use Adobe CC I'm not sure I can download two different systems for my monthly subscription. Mind you I could use Canon's DPP to view the files.
Alternatively I could just settle for the camera card storage I have which is around 528GB's and delete as I go along if I need more space. Not ideal if I do need extra space.
The final solution is to buy cheaper SD cards for storage and use a back up camera with an SD slot to transfer from CF to SD. I can't see that as being the best way forward at all.
Edited by Dave Williams, 10 January 2017 - 02:16 PM.