[passerine]

I don't have any experience with using Ghostscript as a post-processing step, and I am curious to know if it works well for complex documents.

LaTeX does have a native way of generating PDF-A compliant documents, using the pdf-x package. It's still in beta, but it is quite stable and works very well. The advantage of enforcing PDF-A compliance using native LaTeX is that it allows you to take the further step of implementing reproducible builds. Once that is done, you can be certain that given a LaTeX source file, you will be able to generate a bit-for-bit identical document.

Additional post-processing steps will have to be at least documented, and will probably tie the output on the specific version of your post-processor.