Entrepreneur. Published Inventor. Startup Doer and Advisor.
Theil invested 500k when Facebook had 9mn users. If you have that, you can raise way more and faster.
Historic examples don't help.
If you don't have anything developed, you can give away up to 15%, but the days of investing in companies who don't have a product market fit are pretty much over.
Only the hot spaces.
If your early stage idea can be stolen in 1 conversation than you have a very bad idea. You are an SF resident, you must know the values of the Valley revolve around execution, not just concepts.
If you are working on some very special technology then don't worry. Nobody will care until you make it and show it
Typical pre-seed (100-500k) is 5-15%
Seed (500k-2M) is up to 25%
And over depends.
The "potential of the next FB...." is just that, a potential. Don't fight over equity early but make sure you never give up more than 15%, don't offer board seats too early and no "right of first refusal" or "right of next round lead"