PAXboy.... Could you perhaps tell us more about why you need to know these things. Is it from a technical point of view or a flying technique point of view?
E.g, regarding your first question:
"1) Departure: From idle to take-off RPMs on a 73-400 or similar?"
Are you aware that most procedures call for the engines to be stabilised at a power setting lower than takeoff power before full thrust is selected? E.g. 1.1 EPR or perhaps 70% N1. If you want to know how fast it takes from Ground Idle directly to TO thrust, it might be better to ask this question in the Engineers forum (Engineers do slam acceleration tests as part of their engine tests).
Yes, most, if not all jet aircraft have an Approach (or "High" or "Flight") idle, because of the time it takes for a jet engine to spool up to full thrust for a Go Around. This is normally inbuilt into the engine control system logic (Unless the Approach/Ground idle system is faulty, you wouldn't need to worry about setting the idle thrust higher than normal... The thrust lever position Vs engine rpm settings are adjusted automatically). But, as 777AV8R says, your engines shouldn't be at idle during the approach anyway. It's only in the last 25 feet or so (varies with aircraft type) you would pull the thust levers smoothly back to the idle position for touchdown*. The Approach Idle setting is cancelled a few seconds after landing (unless the reversers are being used).
*It's important to have your levers at idle at touchdown as your stopping aids will not work with the engines out of idle (speedbrakes, thrust reversers, autobrakes).
Hope this helps.
Rgds.
Q.