[Blue15ColoradoLT]

First thing - the Big 3 upgrade

Second thing, there is a small grommet underneath the driver side part of the dash, that allows you to run wires from inside the cab into the engine bay. This grommet is actually about 2 inches in length, maybe 1 1/2 inches in width.

I run my power wire through there and then under the door sills to the back of my extended cab to my distribution block:

As for wire length, you can get a standard dual amp kit with all wires that you will need. Those wires should actually be longer than you need and will sound best if you trim them down to only your desired lengths.