UNI,
Keep in mind, I only know what you've told me, so you could be a rookie or about a 12 yr vet. So, I'll offer my opinion on your situation and you may take it FWIW.
First off, I'm also a younger/smaller looking official but have been around long enough to gain respect where needed. With that being said, impressions do get made regardless, by fans and coaches and I do somewhat agree that it's easier to get "worked" when you look younger. So things that help with that are trying to be the "R" more often than not. Work on your pre-game conference and impress coaches with a thorough speech. Work on good mechanics and a strong confident whistle. Show confidence in your calls and obviously knowledge of the rules and applying them correctly is paramount. With those things in place, any poor first impressions should be gone a few plays into the game.
Onto your situation and 4 questions...
While the comments from the assistant are not warranted in the least, you may have been better off halting play on the next dead ball and having a short discussion with the head coach in regards to his bench personnel. Something along the lines of "Coach, please take control of your bench/assistant. We're not going to listen to anymore of their comments before issuing a technical and that will also result in an indirect against you."
As for the HC technical, I would suggest using a different set of words for the coach in that situation. Again, his actions were also unwarranted and disrespectful and his statement is incorrect as he's implying that you're not paying attention to the game, while also implying that his bench can basically do whatever they want as you're not supposed to pay attention to them. But, even though it wasn't your intent, your original statement could come off as threatening or derogatory. Something better might be, "Coach...please go back to your bench." But would this have avoided the T? Who knows? Honestly, if he was already face to face with you, there is no excuse for that at all. You could've backed up or walked away after administering the technical and if the coach expresses that he'd like to discuss it then, you can appease him but only if he agrees to do so in a decent manner. Going back to my first point...had you informed him earlier about his bench personnel, you'd have 120% justification for the technical and he'd have nothing to question you about.
So...were both justified?
Maybe both could've been avoided, but were you wrong in calling both? No.
And depending on timing, your partner could've switched with you to take some heat off you and move you away from the coach. But things happen quickly on the court, and you also don't want to leave 10 players unattended.
Things like that can sometimes be difficult with only 2 officials.
You could've brought the situation up post-game with your partner and get his take on it. Take his opinion with a grain of salt, just as you would any other official and determine if it's worthwhile.
Also, you honestly don't owe anything to the coach post-game, even in a JV game. And this goes along with confidence in your calls. Right or wrong, that's how you saw it, that's how you called it, move on, game on, game over. Your area may be different, but we leave the court immediately once the horn sounds (an obviously if we're positive the game ended correctly)
Coaches are strange birds...when talking to them, you don't want to be the guy who ignores them completely. But you also don't need to give them a thesis on why you called what you did. I always let them know, "quick questions/quick answers". I've heard others say, "Coach, do you have a question?" If not, then we have nothing to discuss. When coaches ask questions, they deserve answers. But when they're just spouting off at the mouth, there are fine lines and key words that warrant penalties. But also, if you are discussing with coaches, avoid certain key words as well.
If you felt the need to appease him post-game or even when he questioned the bench technical, "Coach, I had heard enough from your bench and didn't like their last comment that questioned our judgement on calls."
And LOL at him thinking he can say whatever he wants because he adds 'sir' to the end. Reminds me of Ricky Bobby....
https://www.youtube.com/watch?v=Af-Id_fuXFA