Elad050,
First decide WHY you want/need a business plan and construct it accordingly.
One you write for yourself is quite different than one for investors and/or financing. Either way, it is a useful exercise.
Numbers? Those are secondary. Either you know how to develop a business or you don't. If you do, as time passes, the numbers will take care of themselves. You will eventually learn the reality of it all -- a business plan has no magic to it, it's about the execution of a philosophy or a set of core values, it is these core concepts that you always want to revert to when you wonder if you are being true to your plan.