I would do all 3.
I would have PURP first, Sabotage followed by Tube Screaming Preamp.
While subjective I would probably keep the order switching between the PURP and the Sabotage for two reasons.
- Pregain and postgain Boost switching will provide more tonal variety in my opinion.
- Another option to just using the Tubescreaming preamp as a standard Tubescreamer you could also dial the Gain down and also use it as a Post Sabotage boost with added Tone control.
That is just a quick imagining of a setup.
I also like all the tonal opportunities that would fit into a single enclosure.
I hope that helps.