12v wire through fire wall

So I finally have time to wire in a bunch of lights and junk that Ive been putting off.

I know there is a bundle of wires that pass through the fire wall (hopefully I can find them), one is supposed to be 12v constant the other 12v with the key.

So I have three items that need to be on with the key: trailer brake, mirror heat and eventually gauges.

Three constant ones: fog lights, off-road light bar, and caution strobe.

The lights/strobe and mirror heat will be on switches. Will the 12v wires carry enough load if I have all the junk on at the same time? Or should I find different power sources for each?

There's write ups of using a small fuse box out of, I think, a ford ranger and mounting it under the hood.

That's not a bad idea.

How about how the heck to wire a 5 pin connector?