Hi Addison,
A. This is actually a behavior of the individual user account, not anything with Workflow or Forms. When a user imports a JPG, BMP, etc the file is automatically converted to TIF and saved as a Laserfiche document by default. To change this, figure out which user account is being used for the save to repository step (in forms, double click the save to repository activity and check the Repository profile that is being used. In Workflow, click in the workflow but not on a specific activity to see which profile is being used). Sign in as this user to the desktop or web client, navigate the top menu bar to tools > options > new documents > file conversion and delete JPG and JPEG from the list of files that will convert to TIF. Note that this is a global setting for that user account.

B. As far as I know, you can't convert a TIF to a PDF while it's still in the repository. It can be converted automatically on export, though.
C. The reason you're getting duplicates is because the entries you are emailing have both an electronic document and a Laserfiche document as part of the same entry. If they contain the same information, there's not really a good reason to have both in your repository in the first place since it just takes up twice the space. You can set up some new rules so that if a PDF is added to the repository, the client converts it to a Laserfiche document and deletes the PDF automatically on import. You can find this setting in the client tools > options > new document > Settings > When Importing PDFs: Generate Laserfiche pages(checked) Keep original PDF files (unchecked). This setting is per user but global for that account, so keep that in mind.

Hope that helped. What I recommended above is a "going forward" solution that will keep you from double saving documents in one entry in the future, but doesn't easily solve your problem with documents that are already in the repository. If you want to delete the electronic files associated with an entry that already has LF pages, select the entry and go to tasks > Delete electronic files:

Hope that helps clear some things up. Unfortunately I don't think there's an easy way to select "When entry has an electronic file and LF Pages, only include one or the other" in workflow which would be ideal for what you're asking