I'm curious as to how you outline. For me, outlining and worldbuilding doesn't drain me of the energy to write, but gives me the energy to write. Of course, I have a very loose style of outlining, just jotting down a few major points that I want to hit on a piece of scratch paper. But having that physical skeleton of a scene or story in front of me feels me with enthusiasm as I can't wait to flesh it out into a complete story.
As for being constricting, it hardly is at all, for me anyway. The outline only tells me what I wanted to write down anyway, but it helps me to see in which direction I need the story to go and what essential plot points I need to hit. It would be a shame to forget to mention the Chekhov's Gun
I need to resolve the main plot just because I want to get to the main plot quicker. It also helps to think of the outline as just a general guideline. There is no reason that you have to stay accurate to the outline if you feel the inspiration to do something different while writing, which has happened to me several times.
I would suggest a very loose style of outlining combined with the seat of the pants writing. (Never heard it referred to as pantsing before, but I eventually figured out what you were referring to.) For me, I just outline a little, then write a little, then outline then write. I don't spend a whole lot of time outlining, but use it as a guide to help me hit the points that I want to hit, but while writing, I just let the story takes me where it wants to go. Should the story stray from the outline, I adjust the outline, then continue writing.