Of course it you're a lefty you may want to consider your left thumb. Come to think of it, both thumbs compliment each other quite nicely. If you throw the rest of your hands in the mix, you're unstoppable. Seriously, your bare hands will do most of the work when shaping and molding. The rest of the tools will help you iron out the details.
Damp leather soaks in dirt and oil like there's no tomorrow.
As far as cutting leather, I use different tools for different cuts. For long straight cuts, as in preparing the initial rectangular sheet, I go with a heavy metal ruler and a large Stanley blade. It delivers an exact, powerful cut. For large curves I use shears or tailor's scissors. They give you greater control in creating a smooth rounded edge.