1) That would apply if he actually countered during the tremor but instead countered when the water was coming at him so he would be on the ground, crouched over most likely. Since he is on the ground, forming hand seals would be difficult but the basic earth style jutsu requires no hand seals so using that jutsu to avoid the initial water is fine.
2) You would have stopped your World Shaking when he defended so the quake would have no effect on the pillar. Even if it did, the pillar woulnt be affected that much, it's made from the Earth so it would be shaking as well but not causing it to fall apart.
3) He never said his pillars were that large, just that his height reached was 15 feet which is a major exaggeration. The pillars, if used to avoid something, won't bring you that high.
4) A B-Rank lightning jutsu that is only meant to electrocute lightning can't cause major damage such as a killing electric current of electricity, it would only result in a major shock or a numbing but not killing him. Nagashi, an A-Rank lightning jutsu, doesn't have killing abilities so why would a wave of lower ranking lightning that is meant for passing an electrical current through water be more effective and result in a kill?
Anyways, you should just continue with him avoiding the water and then being shocked. Also sorry for any typos, on phone.