I agree with Bob... work closely with your fire guy on this one.
The trip mechanism will usually have two sets of contacts. One set is used in the "normally open" position by the alarm guy; the other is for you.
I use the "normally closed" contacts to interrupt power to my contactor coils. System trips, coils stop working, contactors open, stuff shuts down.
I have had the issue of the exhaust fans go both ways. The make-up air, any power under the hood, hood lights, and the gas valve (if electric- most are mechanical) all get shut off.
Usually, I will use an 8x8 gutter to mount my contactors in. I do this, as usually the power to the various items comes from different panels.
The coils really ought to be on their own dedicated circuit. This is both because it makes it easy to test the system, and you really don't want any nuisance tripping. Lose power, everything under the hood gets shut down.
As for the circuits being interrupted, I cut into them wherever it's most convenient. This could very well be at the panel, and nowhere near the appliance at all.