If my players create new Characters with the Pathfinder book, and I run them through a 3.5 Module, will their characters be too powerful for the module?
From personal experience, not really. The Pathfinder allows longer adventures without having to rest as often thanks to increased spell use, but I have not noticed a world of difference as to combat difficulty. The changes in classes, while making them a tad improved over 3.5, are really for balance in the classes.
You may wish to implement one or two features such as "channel negative energy" for the enemy clerics for a challenge, but it’s not necessary.
From personal experience, not really. The Pathfinder allows longer adventures without having to rest as often thanks to increased spell use, but I have not noticed a world of difference as to combat difficulty. The changes in classes, while making them a tad improved over 3.5, are really for balance in the classes.
You may wish to implement one or two features such as "channel negative energy" for the enemy clerics for a challenge, but it’s not necessary.
References :
Playtested Pathfinder beta and (ongoing) final rules with 3.5 modules, levels 1-8.