Feel free to pm me if you want further info
We did do this shortly after bringing our boys home - --- and I, like you, feel that it really DID reassure our kids that their birthmom was safe, that she wasnt coming to take them away (her letters were very reassuring) and when they had questions I could ask her them.
When we started contact almost 5 years ago now - we did use an out of state address through a 3rd party. It worked well for a while - but then we gave our home address, and that has also worked well.
I STRONGLY feel it has helped my kids to see the "real" her (weaknesses and all) rather than maintaining a fantasy. I love that I can say ... your beautiful smile comes from your birthmom, or see you eat lots of chicken now, just like you did when you were a baby.
Initially our deal was that I would send pictures every time they sent me pictures (ie send me a baby pic, I send you a current pic). But the more I thought about it the more I realized that I needed to do contact with them NOT because of what I could get out of it but becuase of what it models for my kids - integrity, respect for their birthfamily (thus them etc).
So now, I regularly send pictures and updates and we irregularly get letters or the odd phone call from their birthfamily. We would LOVE for it to be more regular.
I also put myself in their shoes. My kids birthparents didnt really know any other way. They did what they knew in order to survive and because of it they have paid the HIGHEST price possible - they lost their kids. If me sending them some pictures and regular updates helps them to face what htey have lost - heal and then grow into people my kids can be proud of... then I have helped my kids ultimately. That is my job.
I would add however, that even 5 years after initializing contact, my kids are still TOTALLY comfortable that all contact goes through me. I do all the writing, I send and receive all the pics - I initiate all the calls. The boys do NOT want direct contact yet but value what we do have.
When THEY ask for direct contact then we will do our best to facilitate this. And IF they would of asked for direct contact before our bond was fully established (at least a couple of years) I would of said not yet.