In answer to the first question about adding warm cream to warm chocolate your desired combined temp is too much and it breaks, maybe try lowering the temp of the cream. The way I do it with 85 degree C cream onto solid room temp chocolate.
As for the reason not to boil cream, well I read this somewhere and then in my head my reasoning was that the hotter you heat cream the more the proteins denature (unravel) and then when they cool again they agregate with other proteins. And if your emulsion (ganache)is stabilised by the proteins then changing their form is likely to change their ability to stabilise the emulsion. Also practically this works very well, before when I used boiled cream, quite often I would have the ganache break, implementing the method of not boiling cream and only taking it to 85 degrees C I don't have a problem anymore.