tweeter series/parallel

I have a HU that outputs 20 RMS to each speaker, it recently shorted ,some how, from the right front and right back speaker outputs. Now I use one channel to drive three speakers in parrallel wich are two 4 ohm pioneers rated at 20 RMS and the other a rockford/fg cone type tweeter in the middle upper part of my dash don't know the specs to the tweeter. I also have an amp bridged to a rockford/fg 15" sub rated at 150-300 RMS connected via HU.

My old setup when the HU worked right was left(front+back) speakers both at 4ohms each, right(front+back) 4ohms each, and the amp with the sub.

What draw backs if any will my HU have like over heating or EMF?

Will wiring them in series be better wich would be 6 to 8 ohms instead of 1.3 ohms in parrallel?

Would having the back speakers in my old setup and using the amp short out my channels since they both use the same rear channel?

^^^Right.  Dude, you have one big drawback here.  The deck is the brains of the audio system and if that ain't working then you will have nothing but...

Start over.  A working deck and one 4-ohm speaker load per channel.

Thanks guys, kinda figured the 1 ohm was bad for the HU.

So with a new HU will I be able to set up what I had before,

2-(4 ohm, 20 RMS) front speakers, 2-(4 ohm, 23 RMS) back speakers, an amp bridged and the sub(150-300RMS).

I heard of a three way device for this sort of setup(tri-mode) would it be better?