I'll try. Calibrated airspeed refers to a "real" value and not the one that is displayed in front of you. The ASI is subject to so many errors, which vary by aircraft and instrument that the manuafacturer has to be able to put a line in the sand somehere. But as we can't see CAS our limitations are based on IAS (a figure we can see) and thus allow for errors in the airspeed indicating system.
The take off phase, as far as I am concerned ends at 1,500' feet above the airfield from which I have departed. My maximum departure altitude is 8,000' so therefore the maximum altitude at which my takeoff phase finishes would normally be 9,500' For a light twin, I'd guess that it would be once you have got to Blue Line speed - but that's a guess. Your own aircraft limitations should be in the aircraft's handbook.
As for Vmc max. at 1.2 Vs, consider what this value is - the minimum speed that you can control your aircraft following a sudden failure of one engine with the other set at take-off power. Put some numbers in, say you stall at 65 KIAS, are climbing at 90 kts (sounds reasonable for a big twin, even a very light F50!) and an engine fails. But if you had a Vmc of 1.5 Vs, you would have to accelerate (single engine), to 99 kts, not descending as you do so and allowing the aircraft to go where it wants untill you had sufficient airspeed to regain control. With a Vmc of 1.2 Vs, you would already be at Vmc and you'll be in control. But believe me, an aircraft with a Vmc of 1.2 Vs would still be a pig to fly following an engine failure.
Such aircraft are not fitted seat belts. Your bum cheeks would grip the seat cushion so hard as to make them superflous