Answer: retain experienced counsel to assist you.

> I just got an offer from a late-stage startup, that is offering me a small number of shares at a strong price (the latest valuation is already 2x the strike price I would get).

If you are being offered options with an exercise price less than their fair market value (as established by the company's latest 409A valuation), you could face adverse tax consequences. It is unusual for a company to offer discounted stock options, so this suggests that you either don't understand what you have been offered (most likely scenario) or that the company is intentionally or unintentionally exposing you to a huge tax headache (least likely scenario). In either case, you'd be wise to seek professional advice.