No matter how you slice it, there is no perfect conversion to/from DGN/DWG. DXF files have little bearing on the problem.
Microstation can read/write .DWG files, -or- are you having to provide DGN to fulfill a contract? If the latter, you will probably find that it's better to do the work in the required file format up front than to try and convert later.
There are batch converters out there (google it), or AutoCAD Map can directly export DGN files.
Regardless of how it's done, expect problems.