Well, as far as the 2nd baby for you goes, I was delighted that the adoptive parents we chose already had a child, so my little one would have a big sister.
My first post-adoption baby was born 2.5 years after my adopted baby. The keeping part didn't scare me as I had a child who was 4.5 already when my little one was adopted...
The baby born after the adoption WAS a girl - like my adopted baby though - and I had a terrible time bonding with her both during and after the pregnancy. We still have issues today and she is 9 - but I think some of that could be the typical mother-daughter headbutting.
I just had another baby - a boy - who is 8 mos now, and I still catch myself staring at him in wonder and thinking of all I missed with my little girl who was adopted.
There is definitely difficulty there - every 'first' reminds me of what I missed. There's joy in it all, don't get me wrong - but underneath that is a sort of grief that I don't even know how to describe.