Investigation into a cohesive 'set' of cards

How am I going to make my series of cards a cohesive set?

•   The message will be similar on each card, this will force my cards to have similar elements.
• I could use the same font throughout my cards
• Create a logo
• The backs will have the same layout
• Use a limited colour palette
• Once I have decided on style this should be repeated in each card
• Use the idea of the chemical makeup or micro-organisms throughout

What are some more unique ideas to make my cards appealing?

•  A line that runs through all my cards to form an interesting shape when they are all placed together. (Perhaps a line of conditioner or some liquid product)
• Make the physical card an unrecognisable shape that only makes sense when they are in a set, like a puzzle
• Do something 3D or tactile to each card
• Do fold lines on each with instructions to make an origami shape with each card so the audience is left with a sense of achievement and objects that they might like to keep like a souvenir.