Start by checking this pretty collection of examples
You can also try this section
You can also search the How do i forum section with many helpful resources if things fail.
And you can even try animate the boss with Spriter which can import with it plugin the animation directly into construct2 good for specifying body part weak points and animating the whole boss movement routine.
As for the lifebar, how about something like this?
The bullets should have a bullet behavior to start with. It would be a good idea to check the manual section to learn the behaviors and expressions used in the game engine. Perhaps this all would be a good "start"