Yes depending on your car make n model you may need a after market faceplate ... mine cost me about 700.00 Radio with Face plates plugs harness install
No, this unit is strictly to receive the XM/Sirius signal from either a satellite or terrestrial signal (if the location you are in has towers) then the signal is sent to your stereo via FM signal or audio cable if your stereo is so equipt.
I'm not sure what you have currently in your Lexus however I installed it in a Porsche with no issue running Boston acoustics speakers and it is more than enough. The only drawback with this unit is the display color. It does not change and it clashes. It can be somewhat annoying with the rest of the interior lighting at night. Other than that it is a great Unit and pairs very well with my iPhone 6. I just installed a new unit in my BMW and would've gone with this unit if the display changed color. Instead I went with a Sony unit with a built-in amplifier and more money simply because the display changed to match my interior lighting.