How does going IPO changes a company's structure?

Do venture capitalists leave the company and board of directors after getting their 10x returns. how much ownership does company give to the stock holders and what kind of board of directors do public select and what kind of say it has in selecting/replacing CEO.

After going IPO how does the fluctation of stock price affect the cash/revenue of the company?

Having once been CEO of a small public company, my very abbreviated answers are as follows:

1. VCs leave? It depends. In many cases yes particularly if the fund that they used to invest in your company is nearing its life end.
2. Ownership to stock holders? The company doesn't give ownership in an IPO. Ownership is determined by the amount of stock purchased by a stockholder in the offering and aftermarket. (Or maybe I'm not understanding your question?)
3. Board of directors? Public companies must comply with Sarbanes-Oxley. As a rough guideline, they will prefer to have at most 1-2 inside management directors (CEO and maybe CFO) and they will want sufficient independent directors to chair audit, remuneration, and maybe a governance committee. Appointment and election of directors is done via shareholder vote.
4. Board say in CEO selection/replacement? 100%. Of course, a CEO's leverage is based on how well he/she is performing. What constitutes performance must be defined.
5. Stock price impact on company cash/revenue? Zero except when the company is actually offering additional stock. Cash comes in the door at time of offering. AFter that the fluctuations only impact the value of the stock held by the stockholders, which is why investors are fixated on stock price. The other reason is that if the stock price drops too low, the company may then become a takeover candidate.

I can't speak to all of your issues, but I can tell you from working in one company that went public and another that was preparing to, that an IPO changes everything drastically. Quarterly financial results become a driving factor. Employees can't talk about plans that haven't been announced (without the appropriate disclaimers). Its a big change from a private company.

Typically, VC's will leave the board once they have their exit. Some do stay but usually, a publicly traded company will recruit board members with different talents for the next evolution of operations (i.e. growth).

Stock price does not really affect the cash/revenue of a company. Rather, cash/revenue affects the stock price, among other things. Stock price is really a bet on the future growth of the company, what analysts think the industry will do and if investors believe in the CEO's vision.

After an IPO, the ownership retained by the company depends a lot on what is offered via the IPO. It could be 20% or 80%. It really varies depending on the company.

Jeff's comment is a good one. Due to the SEC and Sarbanes-Oxley, a public company has a lot of restrictions, auditing and liability issues that it must look out for. Since investors want returns, CEO's tend to focus on the next two quarters out and push for profit and growth in the near term. This makes any sort of long term plans difficult to implement but not impossible.