40,000 decimal numbers is about 16 KB of RAM (40K * log2(10) / 8). That’s 1980s home computer territory — there’s no way that amount of memory would have been needed for anything. (Given today’s understanding of efficient algorithms.)
Also, the 40 or 50 digit decimal number thing comes partly from not being clear on how to manage scaling "However, by inserting an imaginary divider between the same two figure wheels of all variable number columns, thus making all coefficients and numbers within the Store possess the same number of decimal places, decimals could be used."[1] So there was one decimal point location for all memory locations. Babbage apparently didn't include a general shift function, which is necessary for rescaling results. If you can shift to discard low order digits, as on mechanical desk calculators, you need maybe 10 digits, and a 20 digit product register, so you can multiply two 10-digit numbers and then round off or truncate the result. Without that, you need a lot more digits to avoid overflow. So close...
Useful programmable calculators from the 1970s had 20 to 100 memory locations, each capable of maybe 10 digits. A base Babbage machine with 200 digit wheels of memory, expandable to 1000, would probably have been feasible and moderately useful. Useful for cranking out navigation and gunnery tables, at least. Babbage's difference engine has about that much storage. So that was probably buildable as a minimum viable product.
[1] https://cs.stanford.edu/people/eroberts/courses/soco/project...
The Ingersoll dollar watch (1896), "The Watch that made the Dollar Famous", was probably the first high-volume mass produced product with part complexity and precision comparable to what Babbage needed. A few years later, the Computing-Tabulating-Recording company, the predecessor of IBM, was manufacturing the first commercial electromechanical computing devices in quantity. After that, there was steady progress.
Those were the days when New England was to the world what Guangdong is now.
If you can scale into a reasonable range for each data type, you don't need 50 digits. But that's an abstraction which came decades after Babbage.