You're not the first and won't be the last!
I can't comment on specifics as I'm not familiar with the Nikon line-up. You asked if it would keep auto focus with a teleconverter - with Canon this depends on your camera body and the aperture the lens has with the converter attached.
I know it's all complicated at the start, but if you are not clear no things like aperture etc, I'd suggest becoming familiar with that before you buy anything else. It will stop you spending money on something you may not want, and will give you a better understanding of what your current kit can do giving your better pictures.
Al