I have kept betta fish since 1998. My longest living one was 10 years old when he passed away. Had a couple reach 5 years, as well. One of my 5 year olds was super smart. I like to teach them tricks and have had one that was able to communicate with me via me making a motion that signified a question and him swimming back and forth in 1 of 2 directions. I miss him dearly.
Sororities are cool. Never done one myself. I usually keep one animal per tank, plus a marimo. But I have done ghost shrimp before. Bettas can be mean to them. Depends on the individual fish.
If you have any questions, ask away! Currently have 3 water babies.