its a bit complicated...
I would advice u not taking b5, and playing for e4.
1.d4 Nf6 2.c4 c5 3.d5 b5 and now, 4.Qc2, idea e4 followed by Nf3 and if black takes c4, then developing with Bxc4.
Or 4.Nd2 with also to push e4.
Thats really more simple than taking b5 which leads to highly complicated play.
What is a good to play against the benko gambit?