re: "Speaking to large groups" knower abouters

Some of the most impactful presentations I've seen came from people who weren't particularly polished speakers but those who knew and believed in what they were sharing. So you're already past the biggest hurdle by being comfortable and confident with the subject material. So I bet you'll be fine.

But you do have to get into it and you'll be most anxious at the beginning. Even people who do this routinely deal with anxiety. And without knowing you or specifics of the situation it's difficult to prescribe an approach to kick things off but something light-hearted, anecdotes or similar, are frequently an approach to get over your jitters and lead in to the meat of your presentation. Sometimes just telling them why you're on the agenda is a good way to start. Once you get into your material, face your audience and use your slides only as memory triggers. Your audience can read and listen at the same time so you don't have to read bullet points to them. Ideally you should be able to deliver the same message without slides. At the close, tell your audience the "so what?" outlining what they should take away from your presentation.

I'll be glad to help you if you want. Just let me know how to contact you.