2ohm means you run with 2ohm speakers then you get 80W to use from the amp
4ohm means if you run with 4ohm speakers then you get 60W to use from the amp.

Bridge means combine 2 chnls together to increase available power. For your case, if you combine chnl 3&4 together you get 160W for 1 chnl.

Use normal speaker cable only. Nothing to do with the RCA.

Assuming you are using a 4 chnl amp.

There should be 4 input RCA.

Normally only subwoofers use bridged connections. If you use component speakers with bridging, it wont sound good.

Bridging is by wiring the +- from 1 speaker to 2 different chnls . Example like: from speaker , the + wire go to chnl 3 +, the negative wire goes to chnl 4 - .