Hey there!
Your job made me interested, because at my current workplace I am developing several AutoCAD plugins both in AutoLISP and in autoCAD .net as well. If you need some reference work, I can send you some picture of it with some discription. My plugins mostly modify the ExtendedData of the objects, create labels to lines or different kind of blocks, and things like these. If you can provide more information about the project, I can predict better the amount of time I need to finish the project, but I assume it's not that big work.