for problem 2
the configuration for the script library is right, maybe you can use an absolute path to be sure (${basedir}/src/test/library) because I have already seen some issues when setting relative path when configuring the maven plugin
does the class in your groovy script has a package? if so, you have to add subdirectories to match the package path as you may have done in the scripts directory used by the Soapui GUI
for problem 3
I will release the plugin in a stable version soon (i guess this week). The plugin is available on maven central, so you should be able to use it.
