I'm looking to get a midi footswitch. I'd like the iRig Blue Board to control up & down page turning, and the other 2 switched to control start and advance MP3 changes. Will this work with ST3?

Yes. Make sure you run the blueboard in mode B or C and then connect it as a bluetooth midi device directly in ST3.

    I use one, works great. Set mine to Start/Restart, Volume Up, Volume Down, Next Song.

      No, expression pedals are not supported in version 3. Maybe in version 4.

        Is it possible to assign an on/off switch to one of the Blue Boards' expression pedal inputs to start a track in ST3?

        Maybe. Not sure if the Blueboard works with switch pedals on the expression inputs.

        Blue Board works fine, but the pair light keeps flashing, any way to tune turn this off?

        The bluetooth led will be continuously on once paired with a device if I remember correctly.