My favorite multiple keyboard set-ups are: (1): the arranger at the bottom, with a 61 note piano on top, or (2) Arranger on bottom, Roland synth on top, and 73 note or 88 note piano at my right at 90 degrees from the other two.
Choice depends on the length of a job (I'll bring more equipment for a house job....a lot less for a few hours). Money also influences how much equipment ends up on the stand.
Russ