First, that Pioneer is a good headunit and there is no din1/2 MP3 player.
Second, as far as the power att goes, just put a switch on it. Every deck has a power att or amp turn on lead (blue wire). just splice into that and put a switch and you're in full control.
Lastly, I believe that the fleetwoods have the same dash as the impala's, if so the answer in no it doesnt stick out. You can use the GM 99-3300 kit (metra) and it is a flush mounting kit. This kit is the same as used for cav, lumina. newer s10's, ect.