This is an extremely important email because you are making your first impression. Write it carefully and clearly.. Give the title of the manuscripts, a paragraph overview, your 3-4 major points and why you think this journal would be interested in this topic.
At this point you have given a presentation to a group of knowledgeable people and recorded it. It is time to make a transcript of this recording if you have not done so already. This is the basis for your first draft.
The more published this person is the better but if you cannot get someone who is well known in your field that someone that was in your program or a colleague from your University is certainly good. It is important that they have a knowledge about the publication process. Someone who has never published anything is helpful to an extent but they cannot give you the feedback that you need at this stage about writing, format, presentation, clarity, figures, tables and contribution to the field.
Many of you are better speakers than you are writers. My suggestion for getting your first draft is to do a presentation to someone of your potential manuscript. You may do either a poster session or a conference presentation to a group of knowledgeable persons. This will give you both a first draft and questions that will point out to you where your presentation is not clear.