Yes, these all stack. The amount again will be dependent on your current skill but +3 from potion and +3 from Exceptional = +6 divided by 2 = +3 to the DC

Tomes are Inherent bonuses
Green steel have Exceptional Bonuses
The House D potions are Alchemical Bonuses
A +6 Int item is an Enhancement Bonus
The Abbot trinket has a Profane Bonus

The highest of each applied bonus type will apply and stack with other types.

Kraki