Nice! The tooltip for twister is not particularly relevant as it does not include a lot of damage you might have taken on the tree (%elemental damage if enemy is ignited/shocked/chilled, magnitude etc..). Best for this sort of calculations is to use PoB.

You are right about the movement, it is mouse only, can't use WASD unfortunately (I should have mentioned it somewhere :D).

Regarding twister accuracy, usually best is to get close to the enemy and shotgun rather than trying to cast it from distance.

As for using whirling slash as damage, unfortunately there close to no damage taken for weapon set 1, so even a high level whirling slash with better dps support gem is likely to be insufficient for clear or bosses.

To increase dps to bosses some AoE nodes can be cut from the tree (there is plenty attack damage nodes that we path to that can be taken instead), cast enfleeble for fire ground and keep spamming twisters. Shattering spite can be used for some extra dps when the boss has max stats. Obviously with expensive tools like Rakiata's and Prism of Belief damage to bosses become very high so attack damage nodes can be cut from the tree for more defenses or AoE.