Code Question in regards to 120V / 20 amps
Unless I'm missing something, this is allowed, provided you have enough room in the boxes for the number of conductors coming through and connecting within.  If not, you may need a larger junction box.  For a continuous 20A load, you would need a separate line, but in this case, you are simply attaching a device with a 20A plug that itself provides multiple outlets (not a continuous load).

Since your pool lamp could potentially short or cause other issues (it being near water, etc.), you should consider moving it to another circuit so that you don't risk tripping the breaker on your computer equipment.