whats the max handling of stock speaker copper wires?

Yep. Good old zip cord--the brown stuff that you plug in your bedroom lamp with--is perfectly swell speaker wire. Whoever told you about the rust has been reading audiophile magazines from Planet X. Your analysis of the power-handling capability is very good; light bulbs are a tougher load than speakers, generally.

Now, for very high audio peaks, the small resistance of the wire might cause some slight change in the voltage at the speaker, but you wouldn't be able to hear it. For some reason, people will believe almost anything about speaker wires.

I would say 50-60 watts. Most stock speakers can handle the output of an aftermarket radio (50-55 watts max). I would not go over 60. It's really not whether they can or can't, it's how long they will last at that power.

It's totally fine. People go crazy with speaker wires and wind up bottlenecking them through the terminals anyway. There's a lot of snake oil in the car stereo world.

You'll be totally fine.

i think tahats pretty small though i running 12 awg to normal speakers and im pushing 150 to each because i was getting distortion with stock

it is ok you are no powering woofers

and the rms power is a lot less ,nothing will happend to the wires