About the place to post such questions, feel free to post in your WIP thread. Because such a question is not related to your software, and posting it in this section can prevent some people to read it.
About how to do this front bumper, I agree with ibeam, tell us which car it comes from. The simple picture you posted is not very explicit on the shape of the bumper. Please post a refpic to show us clearly, I'll post a most constructive answer then
To keep on "unconstructive advices", just forget about booleans operation : all they'll get to you is a dirty mesh. And you _never_ want a dirty mesh.
I usually model parts one at a time, just to make sure to complete every detail on a part before moving onto another one. It's more a matter of motivation than a modeling trick. But for parts contiguous one to another, I duplicate the edges making the shared side just to make sure the gap between parts will be nice.
Again, post an explicit refpic (or more), and you'll get more explicit answers !