If you have never used C# or VBA before, this would be extremely ambitious to create within a month and a half, especially if you have any other tasks at all. If you decide to bite it off, I'd recommend the learning resources at cadsharp.com.
CADsharp, the place to go
I think if what you are trying to do is possible, it can be done with C#. The limitations will be the SOLIDWORKS API's, collecting enough definition and automating your steps. Writing code against a 3D model where (virtually) nothing will be the same from part to part is very difficult.
Specific to C#, I would plan on a year or two to learn it (or any language) with enough proficiency to even start on a project like this. What you are asking is not simple and if possible would be very complex.
As an alternative you might be better off with something like multiple macro files that a user can click at each step, or similar. That will help manage the risk of the entire project, as if it can't all be automated, maybe you can do 90%, or 75%, or 50% with various macros. If all the macros work at all the steps *then* you could combine them all together and fully automate your task.
Otherwise what you are doing doesn't look that hard complicated or time consuming from a SOLIDWORKS perspective. I would maybe check to see how many parts you need fixtures for in a given year, compared to how long it'll take you to program a fully automated design method (if possible at all) vs manually designing each one in a consistent fashion, perhaps with some minor macros along the way to help automate a few steps here and there.
Hope that helps, sorry to rain on your parade.
If you can do that, you have your own business. Every manufacturer will use your program.
The programming language doesn't matter. They are all the same.