I think Belarus will enter the war against Ukraine soon.

[Emrys]

3. That'd get Poland's trigger fingers itchy

If the idea were to be any sort of land incursion from the north, they'd have to negotiate bogs and extensive minefields etc., apart from any forces Ukraine's now diverting as a precaution. If it were to take the form of bombardments across the border, that would be another matter, but Belarus is pretty dependent on Russia for armaments, and those aren't in great supply.

As for Belarusian troops, if Lukashenko made any moves as you imagine, I think they'd be quite preoccupied with trying to control their own population.

Lukashenko's hold on power is not cast-iron. I doubt he'd want the complications at this stage, but we'll see.