Finding the cause of a tripping breaker
I would start with the GFCI by shutting off the breaker, opening the receptacle, disconnecting all the wires, separating all the wires, making sure no one would accidentally touch them, then turning the breaker back on. If I got lucky and the breaker didn't trip, I would hook everything there back together except for the GFCI itself and test the breaker again. If the breaker still trips when all the wires in the GFCI receptacle are disconnected, I'd close up that receptacle, and test the other devices similarly until finding the source of the problem. If there are a lot of wires in any receptacle being tested I would use masking tape to label them and draw a diagram showing where each goes. I've learned this the hard way.