Getting the scale right can bedone in two ways.

1. With ObjAction Scaler from the FreeStuff here.

2. File menu, Import/Export settings, Wavefront, then set the Factor.

3. is much better for morphs

4. is quicker for other work, but rounding errors will build up over time.

You can flip normals in C4D, but your probably better doing it when you import in to Poser.

The problem is the way C4D V6 handles .OBJ files.
It helpfully (?) converts groups to seperate meshes on import, but doesn't combine them when exporting. It also doesn't preserve material assignments.
Later versions have improved this behaviour and there are also plugins that do a better job (Spanki's I think is for V7).

I think you can use UVmapper to retain the grouping, but you need to careful when making morphs that involve more than one body part.