I run two of my taps for soda/seltzer only. I think the best thing to do is have about ~20-30ft of line for the soda kegs. I have a dual regulator and keep one for soda at 40psi. Alternatively you can split your primary regulator into a secondary and use the second one for beer at a lower psi. As far as flavor goes I use Accuflex Bev-Seal Ultra Barrier tubing which is glass lined and I have no carry-over.
1. PtE Clone