I'm not from Arturia, but am interested in this new product. I'm keen to get discussion rolling.
Reading the info available currently, it has three modes which I'm not sure whether they can run simultaneously.
The literature says it can feed two midi channels with the sequencer, so you can control as many midi devices as you own, over two channels. But it only has one sequencer on it, so you chain as many midi devices onto it as you have but they will all play the same thing. You can also use the cv and gate outs to control one device that uses those signals, but again it will the same thing. Not that that is bad, I send the same sequence to upto three synths at times, each detuned from the other, though usually it's monosynths doing that.
Being primarily a drum machine, the Rhythm Wolf wouldn't really benefit from the KeyStep. The arp would be great to run the bass synth.
So given your gear, I'd look at it like you have 4 sequences to run 6 instruments, 4 of which are software. The two hardware synths are mono's, so I'd run them from the Circuit given it's lower note per step count. It seems like a waste to run a mono synth from the KeyStep sequencer considering it's 8 notes per step capability. Use that with one of your polysynths.