I want to right click on one or more files in Konqueror and create a new mail with the files as attachments. Is this possible?
Yes, by creating a service menu entry.
In the directory .kde/share/apps/konqueror/servicemenus, relative to your home directory, create a file called sendto.desktop with the following contents:
How do I get Firefox to open mailto-links with KMail and use KMail from Tools/New Message?
For some reason this IMO important configuration setting hasn't made it into the Preferences dialog but it is available: