Did that actually answer his question about what software to use and whether there are any good free ones (that do nudes obviously).
What are the GPU and other specs you are talking about for decentvresults that don't take a week to render?
I don't have any minimum specs. Probably anything that could play PC games in the last decade will get you some kind of minimum level of generation, although if you want higher quality results, you may need something from the last few years. If you're training full models, you may want 12GB+ VRAM, although 16GB+ may be recommended for avoiding issues for certain training parameters.
So a wide range of hardware will give you access to a wide variety of possibilities. I'm personally using a 3080Ti, and Automatic1111's WebUI