I managed to find a couple of similar frames on web search that suggest the 1987 Vintage Cannodale identification could be correct. The really unique way the top-tube intersects the downtube before the head tube makes me think this is a very small frame. I would suggest it's a 1987 SR600 in 48cm
reliable interchangeable parts is a trade secret with tiny insights hidden in places across the internet.
I disagree with that. The information is out there and is not a secret.
Shimano publishes a huge trove of information about their products including detailed specifications and compatibility, with an archive going back to 2004.
SRAM is not so great ...
If you want something utilitarian and practical leaning, the closest thing to your "Thinkpad and not a Macbook" analogy is going to be something from one of the spare-parts-bin-oriented frameset companies like Surly, Soma, etc.
If you want something more mainstream and performance-oriented, you'll just want to avoid bikes with proprietary gimmick ...