I’m skeptical of what HostGator did (or didn’t do).
The full post vs. excerpt thing could be a problem with the theme or with a plugin – neither of which should’ve been affected if they only thing that was done was changing the domain name.
I can’t say what’s going on with the completely blank white page when accessing the Contact page, but that’s often a symptom of a badly behaving plugin. Again, this is something that shouldn’t have been affected by a domain name change.