I would start by kicking off the process of codifying your knowledge. I've used confluence for this, and it's a real art to sit down and work out how to structure your information, the level of detail required, and what should be documented in the first place. I've found that the people I've worked with the went from a technical to managerial role were mostly relied on for that vast technical and organisational knowledge that they had built up over the years.

I'm not sure if you're managing a project, product or divisional team structure, but I would say that no matter what level you're attempting to manage, set some sort of vision for your team to align themselves with. This can cover things such as technical aspirations, or organisational strategic goals.

Trust your team. It doesn't sound like there is any mistrust in your team, but I understand the difficulty in getting over that initial knowledge hump when introducing people to a new domain, especially as an "expert" in the area. Documenting knowledge in clear and concise ways, and making different members of your team experts in certain areas of your knowledge will help them to become more self-sufficient in their quest for knowledge and answers. Consider this an investment.

As a general piece of advice, not aimed at any particular part of your post, you were in the same position as your team members are now not long ago, think about the pain points you had and try to learn from them.