So, I did create a new welcome telegram that implements a lot of what you said here (thanks for the draft TG, btw!).
I wanted the TG to give the impression that I was actually talking to the new nation. Similarly, I also tried to put myself in their shoes and act like I was a new nation. In my design of the TG, I wanted them to ensure that they could first play the base game without thinking that there is so much more they don’t know (but need to know) to play the issues game. From there, when they are settled, the options of what could be done are provided. I think I did that!
I am not sure where we discussed it, but somehow sending a follow-up TG to nations a few days after their founding (so they have time to play the base game) seems like a great option to boost retention.