Is a blowtorch suitable for browning/caramelising steamed food?
Browning with a blowtorch is the standard method for finishing meat and fish cooked sous-vide.  I see no reason why it couldn't also be used for microwaved or steamed dishes, with the caveat that dishes that have too high of a water content will never brown properly (instead, the surface will pop and boil).  I'd advise experimenting a bit, to see which side of the "too much water" each dish is on, and whether simply blotting the surface dries them enough for browning.

UPDATED TO ADD: I'm also going to advise you to get a hardware store blowtorch, not a culinary blowtorch.  A standard plumber's blowtorch is cheaper, and has significantly more flame and a larger fuel tank.