I can't have much caffeine so I only have what's in dark choc and a very infrequent decaff coffee. I agree with everyone else, see how it goes for you. Have you tried redbush tea? Some of them are quite good and you can even get blends now like chai, earl grey, vanilla, and also green redbush. Doesn't taste exactly like black tea but you can have it with milk in the same way (although I like it best with lemon except for the blends).
Re the supplements, you can get decent multivitamins and vit C fairly cheaply and I agree with Molly that of the others chromium is probably the most useful. It's worth keeping an eye for holland and barrett sales too!
I don't know if Holford sells his own range of vitamins but if so I'd be cautious. These proprietary book tie-in brands tend to be VERY expensive and in most cases the standard stuff will be just fine. (one of the ME authors sells a herbal sleep aid for £15-20 that doesn't work any better than a standard product you can buy for £2 for example)
(sorry for the late reply, I only just found my Holford book to see what his recommendations were!)