When to start your own Consultant Company

I would like to someday own my own Computer/IT consultant Company. I would like to hear some opinions on some things like:

How much experience would be enough before even trying to be a consultant?
What are the best Certs to have?(Cisco, MCSE,ect..)
What are average hourly charges?
Do you charge by the hour, or by the project/job?

Any other opinions/suggestions would be very helpful. And anything I may be leaving out like legal stuff, is more than welcome.

Thanks everyone!