@SebGrinke:
I was inspired to start throwing together a Wiki tutorial for this after trying to research and finding not a lot of helpful documentation in the area of fonts. This is a known area that needs some work so for the moment I am currently in the process of getting the rough draft done. I’ll get that up soon, but in the meantime I can help you out here with a few tips for getting some better results for your Font for TextRender Actor.
For your imported Font Texture that was rendered you’ll want to condense everything down to one page. Have you adjust the the Width/height and then reimported the asset? I have not tested this on a OSX, but if there is any problem I have access to a Mac that I can make sure everythign is working.