I'd expect the real founders to be in for no less than 1 / (num founders * 2). But in this context for taking a below market salary (as opposed to forgoing salary entirely), I think he's trying to convey >5%, as opposed to the standard SV lure of around 1-2% for an engineer they want to work for peanuts.

Now that I've said that, hopefully someone more knowledgeable will jump in to correct these numbers.

Depends on the valuation of the co., number of founders, and how many rounds of investment they've done (every round dilutes things). Basically though, if you weren't there when the company was founded, you probably won't have it.

Assuming a YC 3 founder model After 1 or 2 seed rounds, likely 10-20% Decrease by 20-40% per round after

YC chooses >=10%