I use both Reason and Ableton Live as rewire slaves to Cubase. This is, of course, ridiculous, but it’s a lot of fun. My advice from what I’ve learned:
Start with one rewire slave and even though you may be functioning correctly, get used to the idea of it. After you have several projects done with your new rig, then think about another slave.
My opinion is that it’s best to use slave programs for limited purposes, and not try to do everything on them like you might in Cubase. Use the slaves for what they are best at. For example, Cubase’s MIDI sequencing environment by FAR is better that Reason. I don’t even care to learn Reason’s MIDI stuff. Reason does have some nice synths, and the DrRex loop player is always entertaining.