GCFI question

I'm doing a bathroom remodel and in my quest to save some $ i though that if I ran the 20A line to a GCFI outlet, then use the load side of the outlet to run everything else in the bathroom (2 lights and a fan), I could use a regular breaker instead of a GCFI breaker, and still have a GCFI protect bathroom. However, that didn't work. Everytime I would turn on the lights or the fan the GCFI would trip. It would not if I plugged anything in the outlet. I then bypassed the GCFI, and everything worked fine. Yesterday I went and replaced the standard breaker with a $40 GCFI breaker, and everything works perfectly, it doesn't trip. So why would the GCFI outlet trip, but the GCFI breaker not? The total load on that circuit is less then 6A.

 

I am not sure if the sensitivity rating is the same on the brkr gfci as the recept,,, but you could have taken lights and fan ahead of gfci,,, the only thing that needs the protection is the recept. We never put that other stuff on,,, fans seem to trip then often and you dont want lights going out acciently.

 

That's how I'll have it, I'll use the GCFI breaker for the kitchen countertop outlets. It's just strange that this happened.
I have another question I couldn't find an answer in the code book. A friend of mine built a deck on the back of his house, and right now the main power line is only about 6 ft above the deck. Obviously that's not very safe, so we'll move the line high up ( it will have about 12ft above the deck after we're done, although technically it will really be right next to the deck (parallel)). I was going to use a 20ft 4x4 post screwed onto the addition he's building right now, and that will leave almost 5ft of pole unsuported (above the roof edge). Will that be strong enough? The power cable is about 50ft long. Of course the 4x4 will be secured by lag bolts to the building, and it will go all the way down to the ground.