Question 1: How to convert 3phase+Neutral 208VAC supply to 1phase 120VAC? Can I tap off one (any) leg of the 3phase supply and use that to Neutral to get the 120VAC? Or do I have to use all three phases and load each phase similarly to balance the load of the 120VAC equipment across the three phases?

Question 2: We want to step the voltage up from 3phase 208VAC to 3phase 800VAC and the Step up transformer is wired delta, so we just send the 3 phases to the final load right? Or do we have to continue the neutral line to the final load somehow too?