Oh that's so nice of you to write them a letter like that. I'm sure they'll appreciate it!
I understand how moving to a larger town is scary. It's a significant change in your life. However 25000 isn't that large, i suspect there will still be a kind of family type atmosphere. I live in a town of 18000 and it seems everyone knows everyone and people are kind and friendly. So I think it's very possible you'll find good and supportive people in your new home, too.
Fingers crossed that your change goes smoothly and you'll only meet sweet people in your way!