We're still waiting on the new version of the GECK to come out, plus a bunch of other tools, like updated NIFtools for Blender, a new BSA extractor/compressor, etc. It is possible to do some decent modding without the GECK (Moonpath to Elswyr for example), but you would have to deconstruct the game's original assets, rebuild them, and then reconstuct them which is difficult and tedious. As of right now, your C# / C++ skills could be put to better use by helping develop mod tools, if that's something you want to do.