We have one here in Denver that we love - they run with a storyboard and have the kids act out the stories after reading through once. They get them involved moving chairs, carrying things, etc., to satisfy the need for deep pressure. All the kids seem to love it and it is equally enjoyable for adults. Message me if you want more details on it.

One of the biggest things that asd families need is understanding that sometimes our kids make noise. A lot of noise. And when you get asd kids together in a room you can get a chain reaction meltdown that is NOT quiet! If you have a room to hold it in that's a bit removed from the main library floor so library patrons are less apt to complain it might be for the best. Also, a room with a door that can be kept closed is helpful for parents of children who are escapers/runners.
I would say that the biggest thing you need (and it sounds like you might already have it) is a positive, can-do, welcoming attitude where you just understand that asd kiddos do weird unexpected stuff but that's just them and they're amazing kids not in spite of their differences but because of them.

This sounds amazing. Find a way to do this for the families that may be afraid to attend sessions designed for NT families. Check with music therapists too.

Thank you all for the suggestions! I have sent emails to local O/Ts but did not think of music therapists. How would you suggest I let local families know of our new program? I hope to start in September or October, so I have a bit of time. I contacted my local Autism Society, but it is a volunteer organization and no one has had a chance to respond yet.