I can't help with your question specifically, but I had some similar questions being a first time D-30 filer. I ended up just calling the DC Office of Tax and Revenue. I was on hold for quite a while, but when someone finally answered, I basically walked through the form with them to get the answers I needed. I ended up calling twice to clarify some things, and both times they were willing (although maybe a little annoyed) to answer my questions.
