I am sure Jeremy Bullmore has written wise words on this subject.
The difficult part is finding the right partners with similar ambitions.
Founding clients shape new agencies as much as the partners vision
Will, determination and ehtusiasm wins.
Good luck and forewarned is forearmed - as I was told by Dan Widen of W&K - at one point you
will get burnt, everyone does, it comes with running a business and learning how business work, you just have to get over it