Sounds like a typical use of 'keystroke' apps. I use Typinator to insert text ( and images, etc. ) into whatever window I might have open. As far as I know, there is no limit on the size of the insertion. I'd create a blank template for the entire page and assign a specific keystroke/command for it, like ".emailsummary". Enter that text ( minus the quotation marks, of course ) and your blank summary text gets inserted into the email for your editing.
One problem with this, is that you may fail to delete non-required pieces or even add the info in required places. That might not present your work in its best light! To avoid that, you could create smaller insertions for each piece of the email, using a different 'keystroke command/word' for each. That might help make sure you always include the info that's needed. Most of these programs will also insert a date/time/signature/etc. for additional info you always include in a message/document.
I really like <
Typinator>, but there are others. I use it every time I come to TS! And in many other apps, as well.
