I wouldn’t do more than one betta in a 10 or any neons in a 10. Everywhere I’ve seen has said neons need a 20 because they are too active. When doing a betta sorority, you need 5+ females to spread aggression, and a 10 gallon isn’t enough space for that. That being said, you could do a female or male betta with 6-10 micro schooling fish like ember tetras or any type of boraras.
they only get 0.5 to 0.75 inch long so a 10 gallon is fine for them (and they like the same conditions bettas do)! However always have a backup plan because every fish is different and your betta might try to kill everything.
As for plants, you could do water wisteria, water sprite, anubias, java fern, bolbitis, hornwort, or any floating plants!