How did you find this out?
I ask because in every case I'm aware of no one except key people was even aware that they had decided to sell until the deal was done. So either you are a key person or the founders don't know enough to keep this to themselves.
Assuming that your next job is going to be a founder the most important thing for you to do is to build and/or maintain a relationship with the VCs. Both the founders and the investors are going to want to maximize the sale price. you want to be on that team so that when the VCs have an company that needs a solid technical founder they think of you or if you start your own thing you have investors that you can call that already know you can build a product and not freak out while selling the company.
Trying to get at a "seat at the table" could mess that up.
Probably 1-5% if he's the first employee. Less than a percent if he's not unless he got awarded more later or they have an unusual equity situation. 30% is founder territory.
I'm not sure of the exact number but it's somewhere between five and ten percent of the company, in incentive options (I'm not the first employee but a large stake was a condition of my agreeing to join the company in the first place, and they've added to that in two later rounds for various reasons.)
Are you sure they added to it? Even if you got more shares they might be a diluted percentage. "I'm not sure" often means "I've already been screwed and I'm not yet aware of it"... I hope not in your case, but if you don't know the numbers, don't take for granted that they are in your favor (this is the sort of thing you learn from painful experience).
Also be aware that (assuming you have investors) the deal might be structured so that the investors get their money back and your stock options are worthless. Getting a high salary in the acquihire job offer might be your best option.
