Gmail – Looking for starred emails which have disappeared

You can search for a message by size (as in file size). For instance, guessing an average word length of 4 characters, we can search for messages of 2000+ bytes (500+ words):

in:sent larger:2K

Unfortunately, this includes text and attachments. You can exclude attachments with -has:attachment:

in:sent larger:2K -has:attachment

Then you can adjust my 2K guess to get longer message (20K), or shorter (900).

source: Gmail Help: Advanced search

It appears that you have a misunderstanding of one of the best features of Gmail: labels.

Every message when Gmail ingests starts with the Inbox label. You can use filters to add labels to them, or in your case stars. If you tell Gmail to skip the inbox it strips the Inbox label from the message. Messages can have multiple labels, which is a great feature compared to folders.

When you are done working with the message all you have to do is select it and then click Archive, or if the message is already open click Archive. the archive button simply removes the inbox label. There is no need to drag the messages any where. The other labels are still attached to the message.

Removing the inbox label doesn't delete the message, it still exists. They can be found by searching for them using label:mylabelname. All messages not deleted are found in All Mail. You can even use the Multiple Inboxes to quickly focus in on all messages with that label, or just click on the label when you have a message open.