It is possible to supply your own design for the 5-card self-mailer. You can request the layout files and work instructions by e-mail.
Yes that is possible.
That is possible but strongly depends on the size of the gadget. The most important aspect is that it is flat. For example, a pack of chewing gum is not feasible, but it is if an increase is made.
The weight of this direct mail depends on the number of inserts that are packed in the product. Including the four insert cards, this direct mail weighs between 30-40 grams.