Glad to have you helping out with the EclipseLink integration!
http://community.jboss.org/wiki/HackingOnAS7 might be helpful to read (for information on setting up your build environment and dev process in general).
Rather then building AS7 with the "mvn" command, be sure to use the ./build.sh or build.bat file in the AS7 root folder. Doing a
./build.sh clean install
build.bat clean install
should get your build going.
Write back when you are past the build issue.