look up BTI on this forum and follow the directions. In regards to your new worm, I am no bug expert but it looks like a slug. Perhaps you could google slug and click on images and see if that is correct.
Its a slug add salt watch it shrivel. They'll eat your plant. diatomaceous earth around the base kills them too.
For your flies I use sticky paper traps, fans across the top of the pots so the fkers can't fly and scrape the top inch off around the edges of your pot. let it dry out on top.