Hypothesis Involving Planetoid Impacts

Not being a geologist, I am new to this group, but have a hypothesis and I was
wondering if it has been discussed yet by geologists, either here or elsewhere.
 Here is the hypothesis:

1) The early earth was smaller than it is now.  It had a crust floating on top
of a mantle which covered the entire earth.  The crust formed following an
extended period of chemical reactions at the earth's surface.  A possible
example of such a reaction is the hydration of minerals caused by the
absorption of water from the atmosphere.

2) Large planetoids impacted the earth.  The ejecta from one or more of these
collisions coalesced to form the moon.  (This idea is not new.)  A large
quantity of material was also added to the earth's mantle and/or core.  This
caused the earth's volume to increase by a factor of about 5.  The crust was
now distributed over a larger surface area.  Although land now comprises about
29% of the earth's surface, inclusion of continental shelf areas would
correspond to a higher percentage, let's say 35%.  This would cause the radius
of the earth to increase by about 70%.

3) The relatively highly curved crust relieved itself on the now less highly
curved surface by distorting.  Massive cracks may have given rise to long
rivers such as the Mississippi.  In other places, more stress relief may have
caused the formation of wrinkling and faulting to produce various types of
mountain ranges.  The cracking process, in addition to the impacts themselves,
may have caused the crust to break up into continents.

I know that this hypothesis sounds far-fetched, especially considering the vast
amount of material that needed to be added to the earth's mass without
completely destroying it.  But isn't it plausible that high-density meteorites
could have penetrated the crust and gravitated toward the earth's center, while
the punctured crust floated back up to the surface?  If there are links to
refutations of such ideas on the web, I would appreciate knowing about them. 
Thank you for your consideration of this matter.
--
To hear is to forget,
To see is to remember,
To do is to understand.
-- Ancient Chinese proverb