In answer to your question meplusone, our LO has been home a year, so we're roughly a year on exactly from you.
With regard to future contact with FC I would recommend going with the same advice that you get in adoption training about avoiding contact around significant dates, eg. birthdays, mothers day, the year to the day that the child left, etc, as then there's no expectation about when the contact might definitely happen again.
Another thing that worked quite well (just from our experience, others might disagree with this) in the beginning (when we were still texting) was to text about LO reaching milestones. So for example, we sent a message asking FC how they were and then gave a snippet about a milestone, something like, 'I just thought you'd like to know she took her first steps yesterday', and then we'd close with, 'we'll be in touch again with an update in a couple of weeks.' This seemed to reassure FC that we would maintain some contact. We always did make sure we text roughly two weeks later, but we varied the time lapse point saying for example 'I'll text again in a few weeks' etc, and then started to send the odd letter instead, eg. a postcard from our holiday.
If I could offer advice to anyone who might be reading this who is starting intros, I would strongly think about how you are going to 'manage' the emotions of the hand over, especially when existing children are involved. I know that sounds a bit strange, but what I mean is, we just weren't prepared at all for dealing with the Fc relationships/ emotions neither in training nor by our SW, and only when a friend who has adopted advised us not to bring our BC to the handover, did we realise we needed to consider this from everyone's perspective, so the transition was as easy as it could be. Our SW was advising the opposite and saying things like, 'oh the BC will get really excited in the car when they're riding home with their new sibling for the first time- it will be so lovely for you all!' So as the OP noted and was also the experience of my partner, who drove on his own to collect, he reports that it was one of the worst moments of his life. There was crying in the street, sobbing, wailing, holding on to LO ...but completely understandable too of course. FC really did love our LO and for that we'll always be so grateful to them. This wasn't a point in time we would have wanted our BC to remember though, so we're so pleased we organised the hand over as we did.
Again, general advice to all doing intros, I would also be very careful what you 'commit' to in intros week. So very early on FC were saying to us, 'will you keep in contact?' and found ourselves saying, 'yes, of course' while gazing longingly at our new LO and not really listening, as happens when you've become a parent (again). I realise we couldn't have said, 'no', especially as there's this power dynamic to contend with that FC have in intros week, eg. 'they like you- they report good things to the SW', but I think we could have been less gushing in the last two days when we found ourselves nodding and saying 'we absolutely promise to come over again soon.' This actually confused BC a bit as for a couple of weeks, they kept reminding us of this commitment, 'but you said we'd see them again soon!'
To return to your OP though meplusone, the involvement of the SW to set boundaries is a difficult one. So like I said, we had a similar situation, but we did find that involving SW left FC feeling a bit confused, trust between us was compromised somewhat I think, as we'd turned this personal relationship into a professional exchange again. For us, feeling in control ourselves about our future contact with FC felt right, as when SW started managing the situation, feelings felt a bit more fraught, as a middle man was causing confusion, not relaying info correctly, and setting new rules we felt uncomfortable with eg. the 'no replying to texts at all' rule that you've described being advised.
Well, I am seriously rabbiting on now, but I'll just close on adding that it's great to hear your BC and Ac are getting on so beautifully mePlusOne. we have very close age gaps between our three and people warned us of huge fall outs, honeymoon periods ending, delayed jealously, etc, but I'm happy to report that none of that happened (yet!!), and ours got on well from the off too, and continue to do so.