I completely agree with ChrisCarlson that one needs to learn/master .NET basic prior jump into AutoCAD .NET API.
By the way, SheetSet API is exposed as COM API, which you can use with AutoCAD VBA. If you want to work with .NET, you still use SheetSet COM API (.NET interop).
With the task in hand, have you tried to work with ObjectDBX and SheetSet in VBA (since you only mentioned VLISP)? using VBA with ObjectDBX (to processiing drawing without opening in AutoCAD editor) may not be as powerful as using AutoCAD .NET API, but in terms of dealing SheetSet, there would be little difference between using VBA or AutoCAD .NET, because both use the same SheetSet API (COM API). While VBA may not be a good choice for a long term solution, it may just be enough to be the solution of you task, before you are capable of doing meaningful AutoCAD .NET API development.