There’s probably a few ways to speed things up.
First of all, if you can store the address in a custom field (or fields) then you can configure MapPress to automatically generate a map when each post is saved/published using that field as the address. You might need to use a CSV importer or similar tool to re-import the posts if the address isn’t already split out into a field.
Once the maps are created, rather than editing the marker title & body, just go to the MapPress settings and tell the plugin to display the post title for the title and the address for the body for mashups.
If you want to change the display further, or want to display something other than the address when viewing a map for a single post, then you can edit the MapPress template files.
Rather than inserting each map manually, you can just add a do_shortcode to your theme template file. You could also specify width there:
In version 2.40.4 I also added a setting for the default map size as a %. I haven’t released that version yet but if you send me an email I’ll be happy to send you a copy.