The canon is very malleable but from what I’ve read, it’s agreed upon by most people that:
Eyes open for chirpies in about ten or so days and the talking begins usually on the same day.
Most smarty herds in alleys would probably dole out space for designated fluffies by rank.
Smarties would absolutely use one or two toughies as muscle and a personal guard.
Mares roles are typically dependant on how much of a tyrant the smarty is and if she’s a poopie. If the smarty is a psychopathic little dictator (like most), a brown mare is usually the communal rape toy, but if shes got nice colours and is obedient then when not pregnant or lightly pregnant she would probably be designated as a “nummie finda”.
Fluffy hooves are made of a soft leathery skin and their strength is pitiful at best, that being said they could probably throw their weight down and stomp something as big as another fluffy to death, if they put all of their weight behind it.
Humans are a wild card for fluffies due to the fact that the world is populated with abusers, neutrals and hugboxers. And most ferals have figured out that it is safer to typically avoid humans, as they tend to be less naive than the domestic counterpart.
Fluffies in an alleyway would be able to play with trash, play huggy tag and of course fornicate for entertainment.
You know I actually don’t think there is much of an answer for the music question.
Fluffy’s are most definitely afraid of lightning and thunder.
Most feral fluffies tend to die quite young, due to the fact that they have the entire world stacked against them, they’re limited and quite idiotic understanding of the world makes them easy prey, the endless army of human abuser is who reveal in torturing the creatures and most importantly the cruelty of their own kind.
In some stories it is stated that their horns are soft and slightly bendy, while in other writer’s stories we’ve seen the horns be able to damage and kill other fluffy’s and even in a few instances hurt humans.
I hope I have answered your questions in a way that you are satisfied with, but at the end of the day, canon is totally malleable to what you want it to be and I wouldn’t stress too much. It’s your story and you’re totally within your right to do whatever you want with the little goblins. And I can’t wait to read it.