I had a look to your issues and here's my feedback.
ISSUE-1 is JAXB issue, for possible workarounds see e.g.:
If you use Step4 & Step5 to configure MTOM on webservice endpoint,
then you have to properly define org.springframework.spring AS7 module.
I bet your ISSUE-2 is related to the fact this module is not installed at all.
However there's simpler & portable solution that doesn't require org.springframework.spring module
to be installed in AS7 at all in order to enable MTOM on Webservice endpoints.
This portable solution is:
* eliminate Step4 & Step5 and
* annotate SpringCXFMtom with @javax.xml.ws.soap.MTOM annotation instead
At last since you don't have the expected classes in project classpath, you
have to specify fork='true' in wsprovide task in order to fix ISSUE-3.