You could try finishing the text and importing in to or building the model in FreeCad. This has fillet functionality in the "Part" workbench. It is a bit of a learning curve but if you have mastered Blender it will be a breeze and you seem to know exactly what you are doing. You can import .STL files into it and then create a solid from that (again using the "Part" workbench).

We did put together an article on importing text into freecad which should give you some background guidance on how freecad works. It does produce very good printable models.