These links might come in handy. It's the ADO.NET provider for iseries dB2 and has links to the VS Add Ins. I think you need a login to download some of them. And it says that they're looking at a LINQ to iSeries provider via Entity Framework.
To get a description of files, schemas, columns, you can use the views under QSYS2. I noticed some nice views that bring together the physical files and logical files.