Money/Currency/Credit Cards

[bigpond]

Hi Everyone
We are planning a three year trip starting in Africa and are hoping for some advice/tales on this subject.
Most of the websites I've found don't seem to give too much detail on what they did or how they did it so I am guessing it's not worth the worry or if they thought too much about it they wouldn't travel!
Anyway, here are a few things to toss around amongst those who are planning and those who have done an extended trip.
Cash is probably king in Africa so is the USD good to take as a universal currency to get yourself by? Anyway I've made a list of some things but if there is anything you would like to point out or add please let us know as I am sure we're not the only ones thinking about this subject.
1. Is it a good idea to take from the UK a large amount of USD, stash it in safe places around the vehicle and use it along the way or is it easy to get your hands on USD in Africa? I just thought it might be an easy currency to use for some transactions when you don't have any local currency to hand.
2. UK bank charges for withdrawals. We will probably be making lots of small withdrawals because there are lots of countries and we trying not to end up with a whole lot of useless currency. Do these charges become quite an issue?
3. We know that in many countries (except the big cities) that an ATM might be as rare as a UFO but is that still something that has a big impact on cashflow.
4. Do very many places take credit/debit cards in larger cities?
I'm sure there are lots of other things I need to ask but this might be a good start.
Thanks
Barbara