How crunchy is pathfinder 1E on a scale of 1 to 10?

Pathfinder 1e is a sprawling modular megasystem, so how much crunch your experience entails will depend on how many and which optional rulesets you are using. Even within just the core rules, the level of crunch you will need to engage with can vary significantly by class. If it’s your first time running, focus on the core rules, and you can always research and add more options and subsystems in as you become comfortable with them.