Scene increment / loop

I recently built this 'relative' scene launcher to simplify scene automation from my MIDI controller - I just need to launch any scene labelled 'mstr' to be able to launch scenes relative to it from my other, hard-mapped buttons.

I now want to be able to set it up so that my drummer can step through these scenes with one drum-pad - increment the current scene. I'm thinking I need add a 'loop length' to the master scene name, and then use another regexp to extract the number from the end of the scene, so he can loop around a few scenes.

Total noob at this, I wonder if anyone can help me get started? I attach the current scene launching patch - I've added 'post-it' style notes to it that should hopefully make things clearer than my rambling :)