Hi David,
Thank you again for the details!
1. Unfortunately no, because taxonomies are separate objects, and their values are strings – thus cannot be filtered via slider types.
2. I believe you are looking for the display mode feature
3. Yes, you can do that actually. I would say, that if you prefer using sliders, then numeric values are better as custom fields in this case. For string values (like gender), the usage of taxonomies is probably better.
Sorry if I confused you with these before. I am already familiar with these, and sometimes I forgot how confusing it can be. Maybe combining custom fields and taxonomies will be more complicated than I thought.
If you don’t plan to add like tens of thousands of entries, using just custom fields should be still fine, judging by your server setup and performance. I only suggested taxonomies, because I wasn’t considering you wanted to use range sliders for numeric values as well, I overlooked that, my apologies.