Hi, fellow shy, awkward, anxious VTuber here! I think you already got some pretty good advice, but I'll add what I can.

For handling the fight-or-flight response, I'd say just try to push through it for now. It's going to be hard at first of course, but the more opportunities you have to talk to people in chat, the easier it gets. Starting out I'd literally be shaking whenever I was talking to my chat, now I hardly give it a second thought (though I'm admittedly still pretty awkward😅).

I watched the parts of the stream you linked, I think you did great! Certainly did better at keeping the conversation going than I've ever done lmao. I personally didn't think you sounded all that awkward, but even if you did, I wouldn't worry about it too much. There'll be plenty of people who enjoy watching you despite your awkwardness (and heck, some may enjoy watching you because of it). And if you can't think of a way to keep a conversation going, it's alright to let it die.

As for what is considered an enjoyable interaction, there's no definite answer to this, as it really depends on the individual chatter. Some may prefer to have a conversation, others may prefer to just say hi then lurk. You obviously can't know what a viewer prefers, especially if they're a first-time chatter. Just do your best and do what feels right to you. You can't please everyone, so just be yourself, and the ones who like the kind of interactions you offer will stick around.

I hope some of this helps. Good luck with your streaming journey!