Car Stereo Gurus: got an amp for Xmas-- no idea if its good

[WRXD]

Hey-
I just got an amp for Christmas from a family member who knew I was considering upgrading my system. The problem is, I know nothing about car audio or amp specs. I have no idea what type quality amp I recieved was or what other components I would need to make it work.

my car: 04 WRX completely stock system (no factory upgrade)

the amp I recieved(stats in the owners manual):
Crunch car audio 'Ground Pounder' GP1400.4 4 Channel amp
Power output RMS/Dynamic
4ohms: 160x4/175x4
2ohms: 320x4/350x4
4ohms mono bridged: 640x2/700x2
Power Supply: PWM
Configuration: Mosfet
Soft Start Sound: Yes
Dampening Factor: >151
Signal to Noise ratio (A-weight): >95dB
Total Harmonic Distortion: 0.05%
Channel Separation: >72dB
Input Gain Control: 0.2V- 5.0V
Input Inpedence: 47KOhms
Variable Frequency Control: 50Hz-250Hz

so my questions are:

is this a good amp?
what else do I need to buy to use this amp?
can I power a headunit and speakers and not have to have a sub??
is it worth keeping??

thanks in advance...