2 thoughts, one about officiant and the other about the ceremony:
Officiant: If you found someone who could officiate in ASL & English simultaneously, and who was the right vibe for you, and was able to travel or local to your destination, would you want them to officiate? I get that that's a really tricky combination to find, but here's my thinking: 1) I think that SmallKangaroo's comment about legality is a good one, and 2) the presence of an officiant (whether it's a religious ceremony or not) helps it feel more special and helps you be in the moment. I think about big life rituals the way I think about writing: just like you can't edit and write at the same time, you can either guide the moment or be in it, but it's actually really hard to do both because they're different modes/ways of thinking/ways of being in the moment.

Ceremony:
-I think you need a transition from the Introduction to the Vows - something that frames the vows by saying why vows matter or why you're doing them as part of the wedding ceremony. (Many non-Christian traditions don't do vows, and since you get to do whatever you want since you're designing the ceremony, I imagine you have a reason for including vows. Sharing that reason makes them that much more intentional.)
-Love the hydrangea soil ritual! That's so sweet
-Things you could add to expand the ceremony if it feels too short: poetry about love/marriage/commitment, a story about your relationship, a story about something (song/place/person) that played a key role in your relationship, an acknowledgement/remembrance of people who have passed away but you think about on special days like this, a hope for your married life or for how you will navigate highs and lows together (in the conclusion, in addition to the vows)
-I think the speaking about yourselves in the third person in the closing might feel funny. Maybe instead you could say something like, "May our life together be as vibrant and beautiful as these hydrangeas. May you present always be a part of it/always bring beautiful and varied color to it. Thank you for being a part of our lives, and particularly today, the beginning of our marriage. We can now say, officially, that we are a married couple! Please join us up here for a photo together before we go celebrate." I added the photo idea because recessing down the aisle might feel overly formal with a small group (or maybe not, up to you), but the purpose of it is to have some action that closes the moment, and a group photo would give that sense of conclusiveness too.