what thickness should I run to my mids and highs, if im running a 45x4 rms amp (and what size power) and what size power/speaker wire should I run to my sub amp if Im pushing 2 12w6v2 with a t10001bd amp (rated at 1655x1ohm)
Unlike power wires, speakers do not require thick cables. It doesn't carry high current. If you get confused, take a look at your AC household wires. Not many wire strands, not is it thick. Just don't get fooled into buying "monster" cables.
It won't hurt anything. You just might have a slight reduction in power with the increased resistance. 20 gauge is pretty small for 500 watts, but the actual output difference between that and 12 gauge would be pretty difficult to notice by ear.
Say your amp develops 500x1 into a 2 ohm load. I'll spare you the math, but a five foot run of 12 gauge would reduce your amp's power output to about 495 watts. Using the same length of 20 gauge would reduce it to aproximately 472 watts.
That 23 watt difference may seem like a lot, but in real life you'd be hardpressed to notice it.
16 gauge would be a better option as your amp would be developing about 488 watts, only a 7 watt reduction or about 1.3% less output than with the 12 gauge.