1) Avoid taking any pictures from the plane while on the ground until the FAs sit down, where you are not visible.
So, just relax, watch the safety video or demonstration, wait till you here the pilot call for the flight attendants to take their seats for takeoff. When they are all sat down, pull your camera out.
If the F/A's catch you taking pics while on the ground or below 10000 feet, they will tell you not to use it until above 10k. If you do, you are commiting a federal crime.
This way, the F/As never told you directly not to use it, therefore you are not breaking the rules.
2) On decent, wait for the F/As to take their seats on final approach, then pull your camera out and snap away.
3) Cruise is the only 'legal' time you can take pics. But again, on akeoff and landing you can get away with it as long as the F/A's don't see you do it and/or say anythingto you about it.
Just be patient, wait till you are lined up in position and hold on the runway, and then pull the camera out.
About the letter, whenever you feel comfortable, relax and be confident, oh wait, that's talking to a girl you like.
Do it when you feel comfortable, don't do it in a suspicious way (walking up with an akward grin and slip the note into his/her hand). Make it clear they know what is being giving to them, so there is no chance of them thinking you are giving a bomb threat or some National Security crap they could come up with.
Lighten up while you still can, don't even try to understand, just find a place to make your stand and take it easy