The Universe as we know it is only part of The Greater Universe which has no beginning and no end and has existed for ever. "Our" Big Bang was just one of many over the eons of time (time and space which has also existed for ever).

What caused that bang was.... all the Black holes in our Universe eventually consumed each other until everything is in one enormous Black Hole. The immense pressure (gravity) and heat eventually creates "The Big Bang" and off we jolly well go (again).

Is that theory any more outlandish than everything being created from nothing?

A plausible theory but to my mind more difficult to visualise than the theory that at some point something came from nothing.

Your theory presumes that time is infinite in both directions, no beginning, no end.  I find it easier to imagine that at some point time must have started and that the end of time is a matter for conjecture.

With regards to the Higgs Bosun particle as I understand it this is the missing part of the theory regarding how particles gain mass.  The Pluto of quantum physics.