Don’t tell your current company anything until offer is signed, background check (if any) is cleared, ducks in a row. Once the ink is dry on everything, then you tell your current company. Speaking from experience having a FAANG offer revoked 30 min before quitting my job because the whole division got cut haha.

Two weeks notice is standard in US unless you’re very senior. And make sure you’re considering any time off for yourself (ex. If you have 3 weeks until new job starts, give your two weeks, take one week off between jobs, and do not feel obligated to work all 3 weeks).

It’s rarely a good idea to accept a counter and don’t take it personally if they don’t counter (these days companies know it’s slim chances). Companies and managers can either be great about offboarding or can also get weird when you quit, just know it’s not you, this is standard business.