Roasting small chicken
There are a couple of easy steps you could take to ensure crispy skin:


Let the chicken dry uncovered in the fridge overnight (or at least for a couple of hours). This desiccates the skin which will lead to much greater browning on the skin, and if you stuff the cavity with something that will let off steam during cooking, like lemon and herbs, this will not dry the meat out.
Make sure you season the skin generously and add a small pinch of baking soda to the salt before applying. The alkaline property of baking soda speeds up the Maillard reaction, which will lead to more browning in the short cook time.


Lastly, I would stay slow and low with the cook time, although that applies to all roasts.

I have never used a blowtorch and I am curious what effect that would produce. If you do use one please let me know how well it works!