If you fall back on your previous turkey breast and butt smokes, that should give you a good base-line for time on smoking. It will slightly increase your overall cooking time, as the smoker being filled with more meats will take longer to recover chamber temps...once it recovers, you're back to normal, as if only one piece of meat were being smoked. Also, if you open the chamber door to add meats, this will increase the cooking times for the meats that are already in the smoker when more is added.
A couple things to consider with verticals is that each large piece of meat will somewhat baffle heat to the one above it, so you may consider running chamber temps about 20* hotter.
Most will say poultry goes on bottom, due to higher safe cooking internal temps. The turkey should be finished much earlier than the butts, due to lower finished temps (165* minimum recommended), while the butts are taken to ~200* for pulled pork (assuming you're pulling and not slicing).
I don't run electric smokers myself, and every type/brand has varying convection efficiencies, so I can't say just how long yours will actually take.