I have organized a few Baby Welcoming/Birthing Ceremonies for a few different friends of mine, and one of the really nice things that I always try to do is go around in a circle and have everyone talk about their connection to the birthing mother and the new baby. Either how they met, memories they've shared, or hopes they might have for the future. It is nice because people get a chance to share what is in their minds and hearts about welcoming a new being into the community/family, and you don't need to do much to prepare for it beforehand. Sometimes when doing this, we will offer an image ( a mental one, or a physical brought item) to share with the birthing mama that will give her strength on the birth journey. This is the part where we do lots of crying and hugging, and I(we) often try to provide paper so the other women can write down their sentiments for the birthing mama to read and reflect on later.
For instance, at a birthing ceremony I recently organized, my friend brought sprigs from her babies' placenta trees, I shared a stone carving of a woman with a heart which to me represented the idea that women are strong, another friend brought an egg, another friend brought the suggestion of yelling/singing/making noise, that it is sometimes great to let labor roar through you....
And then we finish with a nice potluck and do a dinner sign up to be brought to the mama after the baby comes.
Hope this was somewhat helpful. I don't really have any specific readings to share, but have found that going around the circle is just so amazing, to hear the outpouring of love. Can you tell I love this stuff?
And also, may I say what a great friend you are doing this in your first trimester? I'm not sure I could have managed it.