Hello Eddie,
Long time no see
The .NET learning curve IS considerable.
Become familiar with the framework and IDE.
Become proficient with .NET development in AutoCAD.
Become familiar with the managed wrappers for the ARX functions in AutoCAD.
You may be best served just translating from VBA to .NET retaining the COM/ActiveX usage you are familiar with.
There is some reasonable guidance available in articles at
The AutoDESK Developers Site.
The AutoDESK University Lectures
'ThroughTheInterface' Blog.
We'll leave the C#/VB discussion for a more suitable venue
good fortune !
be well.