"Node Picker" for custom module?
Without knowing the full scope or what modules/custom code you've already developed, this could be done fairly easily with a hook_menu, custom form and a content type. The new content type would have a multi-select (probably auto complete) node reference field which will allow for simple reordering. You could then implement a hook_menu with a custom form returning all the newsletters in a select list and when the form is submitted you can use node_load() to get all the referenced nodes from the selected node. Your submit handler would pass the applicable values to whatever batch mail module/functions you're using.