Thanks gents, for the info.
I found the PDF for the flash from the Metz website shortly after posting.
Reading it and your replies I found the answer to my Q2 and it was because, rather stupidly, I didn't realise the inner wheel was for the ISO. I'm not sure what mine was set to when I last used it but it was not conciously set for the ISO of my film speed, which might explain why I was getting "Hi" errors on my Nikon despite rather low light.
I have read through the manual again and it makes a bit more sense now, I think. So, my light meter reports EV13 which equates to a Hasselblad lens setting of (for example) F8 at 1/125th sec. So I set the ISO on my flash to ' 1" ' (which I think means ISO100 - see question below), and turn the auto dial to F8 for normal flash or say 5.6 for fill in flash providing my subject is between 5 - 7 meters. Then shoot. Is that correct?
Last question - the manual doesn't state this, but the central ISO dial on the flash reads :
ISO 25 50 1" 2" 4" 8" 1"' (i.e. 1 followed by two little dashes, 2 followed by two little dashes and lastly 1 followed by three little dashes). Does that mean :
ISO 25 50 100 200 400 800 1000