Recommendation letters through Interfolio

Hi all! I'm starting to set up Interfolio for my recommendation letters, and I'm a little confused about how to go through the process.

Is it recommended to buy Interfolio premium to check that the letters have all of the requirements (like being on official letterhead)?

Also, is there anything I need to do other than fill out the request form and let my recommenders know that the request is coming?

Thank you guys!