They're all optional, you don't need to do any of them.
I may eventually add a method for making each new puzzle type easier, but that likely wouldn't be for a while, as I'm already in the midst of rendering the next update.
Some quick tips that might help?
Sliding puzzles with the 16th piece missing (such as all the ones in the game) are best worked on from top to bottom.
Match game you could screenshot, phone pic it, or write down the positions.
The final puzzle is more about knowing the game. Some of the questions are easier than others... through trial and error you could eventually memorize most of them, but again, it's probably not worth the effort.