1) Create a views with content type Brands and select Format > Show: Fields. By default you will see a list of the node titles. Sort the results by Title:ascending.
2) Add a Field: Content: Title. Check "Exclude from display", uncheck "Link this field to the original piece of content" and on the Rewrite results select "Trim this field to a maximum length" where set 1. Also in the same section uncheck the "Trim only on a word boundary" and "Add an elipsis" and finally check the "Strip HTML tags".
This will fetch the first letter of each title.
3) Finally on the Format: Unformatted List: Settings use the "Grouping field Nr.1" option and select the latest field you added.
4) Accordion is another issue here. You probably know how to accomplish that task.