1. Inkscape document background color does not export to PDF, but only to PNG. Use rectangle with desired color as background.
2. Inkscape does not support CMYK color mode for printing. Convert text to path, then import/open with Scribus to export PDF in CMYK mode. Text in SVG does not import into Scribus well. But convert text to path seems not to preserve bold style …
3. Save a PDF to CMYK with Inkscape using GhostScript command line tool
4. It seems windows and mac style font size slightly different. Perhaps because of the helvetica they use are different?