Wayang Empiricist Investigator (PFS)

[2 Coppers Worth]

A couple of Questions
1. My build has me at a 19 dex and a 16 int. It looks like rules as written I will be taking a hit to my disable device check cause the wording of ceaseless Observation is that "At 2nd level, an empiricist uses his Intelligence modifier instead of the skill's typical ability for all Disable Device, Perception, Sense Motive, and Use Magic Device checks." Am I correct or can I choose to use the original ability?

2. Alchemy says that it can use any thing from the Formula list in Advanced Players Guide pg 32. Can I use other Alchemist Formulas from other books

[Inspector Pendergast]

It looks like the stat substitute isn't optional. It doesn't use language such as "may".

Investigators use the Alchemist list. The text is just pointing the reader in the direction of the APG, because that's where the Alchemist began.