The BT mic plugs in on the back of the unit. The auto tune mic goes in the 3.5 in the front. It doesn't stay plugged in all the time and its easy to use.
The RCA's on the back are, in fact, inputs.
I'm not sure what you mean about RCA to speaker wire deal, but there is a switch on the unit for you to go between high level outs and low level outs.
Active is is using the crossovers on the HU. You have a ton of control. Crossover points, slopes, individual level control for each set of rcas, polarity, independant left and right EQ.
You also have the convenience of two USB inputs. I used the supplied cable for thumb drives and used my iPhone cable for the other.
There is also a "standard" mode and a "network" mode. They're actually pretty similar but you get more control in "network." Although, there's no sub level in that mode which annoyed me but I just wired in a PAC. No biggie.
It really is a crazy amount of tuning and control for the price. The only thing that comes close is the Clarion cz702. But less EQ and no L/R. You also only get one USB and no auto tune (I think), but you get the option of HD or satellite radio. And it's ~ $100 cheaper.