It’s going to be hard for anyone to properly answer you without knowing what you are trying to achieve musically.
But, I’ve ran/run a similar setup myself, I really like the AR/A4 combo. If you want to keep it minimal, I would run the A4 into the AR so you can use the AR’s compressor across them both.
When I’ve added in a synth for poly duties, the Novation Peak was my default… it always compliments the sound of the Elektrons.
Here’s mine: