I'm inventing a COMPLETE brand-new alphabet - how many letters do I need?

No, the bottom line is that you keep changing the question. Are you asking what the number of discrete phonemes is in every language with 10,000 speakers? Or are you asking how many phonemes the IPA can represent?

Those are two different questions.

The first question can be answered by going to the Wikipedia page of every such language and counting the phonemes and eliminating the duplicates. If you’re that interested in the answer, do it yourself.

The second question has been answered for you repeatedly.

Thank you for your help.

Yes, I have it memorized. The answer is infinity. Thank you for this information also.