Thanks so much for the lovely welcome! I am meeting up with many old friends, so this is really great! I'm reading your post right now and it's very helpful.
About the ISO... it depends on which camera you have, but in general all recent camera bodies are getting better at handling higher ISO. I use the Nikon D750 which is pretty good in this respect, and I will often push the ISO to 1600 for birds. In my experience, you can get away with high ISO unless you decide to brighten the photo or push the shadows too much in post processing... then the noise will often get pretty bad.
I'm happy you like the photo... I just posted a gif made from 9 or 10 stills of this Junco. If interested you can find the gif here: https://steemit.com/photography/@keithboone/a-bird-to-brighten-your-day
It's great to reconnect with you here! Thank you again :)