How to convert .obj file to .stl so I can slice to G-code?
One can import an OBJ file into free program Meshmixer, then export it to STL format. There are other programs that are free and paid (such as Fusion 360) that will perform similar tasks.
As noted by user agarza, Prusa Slicer will import an OBJ and will also export to STL format. PrusaSlicer is also free.