Okay I was assuming you already had quite a collection, my fault ;-)
But honestly: Do you need everything right NOW? Probably not... I think you can plan this out for a longer time. So starting now with Rebels/Empire and later continuing with the other box for example.
Also you could start out with both boxes at once but adding minifigs later on... light starting with the middle line, later the top line, later the buttom line (if you are planing to do these boxes as you did in the picture you shared).
I'd start for example with Yoda, Obi-Wan, Luke, Leia, Han, Chewie, R2D2, C3PO and for the other side Boba Fett,Darth Vader, Palpatine, Red Royal Guard (standing beside Palpatine... so actually the minifigs would stand in line just as I wrote them down ;-) )
Later you expand and put up commanders, death star troopers (I mean the guys who are in the set with the guards... forgot the name xD) etc...
May the Force be with you!