I agree with Lisa.  Preparing taxes isn't much about math, it is about knowing Tax Law and the rules.  Corporations have a bunch of extra stuff, and it is foolish for a business owner to do the corporate taxes themselves (and even more foolish to start a corporation without first sitting down with an experienced tax professional to determine if that is the best way to do things).

As for your question of "Proof of Net Income", that depends on who is asking.  The "proof" is generally the tax return itself (along with Schedule C).  But what "Net Income" numbers they look at depends on who is asking.   It might not be any of those possibilities you listed (they might start with one, but then make adjustments to it based on other things).  That is something that only the one asking for it can answer for you.