Well, this is a pretty broad range of topics. Help me out a bit and tell me what your goals are that you are trying to accomplish regarding sharpening knives. What type of knives are you sharpening and what do you use now? What do you wish to accomplish that you are unsatisfied with using your current equipment and technique?
When you refer to natural stones, could you narrow it down - stones from which country, fine or coarse stones. Are you polishing $5 knives or half million dollar swords or something inbetween?
Are you looking for solutions that cost pennies or thousands of dollars?
Also give us an idea of your skill level.
Are your goals to sharpen your edges or does this also include aesthetic considerations such as traditional Kasumi finishes?
Finally pick the one question you listed that you most want to get answered