Sorry for the delayed response...Been really busy with a lot of things!
There are a few options out there for you..
- Import using Activiti 6 Web Modeler (community)
- Use of Eclipse Plugin (community)
- Using the Alfresco Process Services Web modeler (Enterprise)
Converting them after import really depends on the process model, so I'm unable to provide any advice without seeing the xmls!
The advantage of using the Alfresco Process Services over Community is the standard support + other enterprise only features like stencils and data models which will allow you to build re-usable components that can speed up the migration process. If the processes have a lot of user forms and if you are planning on re-writing the UI, going enterprise can add real value by leveraging the Application Development Framework which we have on top of Process Services. Hope this helps!