I cant answer all your questions, but I do have a pair of the PSB Goldi's . I currently use a older Bryston 4B amp, and I have by times used a pair of 4B's switched to mono mode with them as well (500 watts per side if I recall). Depending how loud you like your music I would stick with either a 4B or a pair of 7B's for the mains and a 3x120 watts (5B ?) for the remaining channels. The PSB's can handle a fair amount of power, it all depends on your listening habits.
Cheers,