I'm starting a new self-designed Pathfinder campaign as the DM and I'm unsure how many combat encounters I should plan each session.

The characters will start at level 1. The group consists of 4 PCs in a well-balanced group. However, the players are only mildly experienced with playing role-playing games. I plan to have them do some investigating in town and some non-combat trap/puzzles in a dungeon in addition to combat. How do I determine how many combat encounters I should run in each session?