You have to work backwards from that note before you begin, or you'll wind up running out of room on top (unless you're Julie Andrews or somebody else with a five-octave range).
Absolutely. I am a baritone/bass and have sung it at several sporting events and dedications. You work out your key by how low, but comfortably, you can sing the third note.
I don't know about other singers, but before I go out onto the court or field or whatever I have the first note humming in the back of my throat. I keep it going, quietly, until it is time to sing. If you get the first three notes correct, the rest is on autopilot.