There are standards for how many independent inputs are needed based on the criticality of the system. It's not just a guess as to how many are sufficient. That's why the categorization of MCAS correctly ('catastrophic' vs. 'hazardous' is important)
No. If you have a hundred AoA sensors, then you know to trust that whatever 90% of them are reporting is the truth. You also know exactly which of the remaining 10% need to be repaired or replaced upon landing.
I'm not sure what you're saying a hard "no" to; that's a strange response to my point. Your response is a little naive in terms of the way sensors work. You won't necessarily know which are reporting "truth" because in reality there will be a range of values reported because each sensor has a bound of uncertainty. It comes down to understanding what level of uncertainty and reliability are necessary for the application.
In designing airframes, there's actually guidance along these lines to remove the ambiguity of how many sensors are necessary. You can use calculations to define what level of reliability is sufficient. As an example to this point, there are standards like IEC 61508 that outline the procedure for doing such calculations. Many organizations also create their own standards (e.g., five redundant sensors for mission critical systems, self-diagnostic sensors for safety critical systems etc.) It shouldn't be guesswork. It's a risk-based decision, not a subjective guess as to whether two or "a hundred" sensors are necessary.