Play By Post is very slow... look for a weekly game using Discord or Roll20. Both are digital platforms that support live chat programs. I think they support voice chat as well... not sure.

My wife picked up some ASL through a 6 week class at church (we have a few deaf people and an interpreter), and my 5 year old is using it when spelling things out. Good stuff. I am low dexterity and can't spell things out very fast. My understanding is that ASL has a smaller total word count than regular written/conversational English. Does that impact playing D&D? I would imagine there's not a standard ASL word for things like "Fireball" or "Mordenkainen's Mansion" or "Aboleth."