how do I configure Roku stick to power on to a specific streaming app (HULU) ?
It's not possible. The best you can do is to move Hulu to the first position on the Home Screen so that it's easy to access, although Roku keeps adding junk above the apps that can't be moved or removed. If you have a remote with a Hulu button, you can press that to take you right to Hulu or, if not, get a Voice Remote Pro that has two programmable buttons.