The contactor looks like a great unit and it looks like they have no problem handling high power!
I do just need some way to make the max temp variable and latch, and that should my circuit almost be able to, I just need to find out the problem as showen in my circuit. :-)
i recommend then making a gross overload safety with a thermostat that is way up there but fire safe, and a secondary adjustable safety that uses electronics. If you want to be really safe put them on separate contactors. or with more thought and analysis you can make a or-gate type circuit that triggers the contactor (but don't actually use transistors with the fire safety)
the main problem I see is that your temperature sensor is running in parallel with wires carrying 100 amps. i have no idea what that can do to a RTD, thermistor, thermocouple or other signal, it sounds kinda bad and like it requires shielding at least, if you can have the signal for the temperature wire come in at a right angle it would be better, but I assume its basically strapped to the main cable via zip ties for the sake of not being ridiculous. The thermostat kind of gets around alot of these problems but its not adjustable or precise. Someone with high current industrial experience can tell you what to expect, I never worked with a crazy circuit that required a signal line routed in parallel with a giant conductor.
But in terms of reliable function I think the contactor is basically a requirement for safety.
Keep in mind the electronics control system connected to the temperature sensor can get a malfunction from spikes possibly, or just get damanged from bad manufacturing or defects or age or whatever (i.e. arcing, surges), so its highly recommended to make it a one way trip that needs a manual reset if triggered so it can't turn it self back on. Another way to do this is to trip a breaker with a contactor that shorts out the supply, like a crowbar circuit, and blows a fuse.
I think the automotive stuff is more dealing with inrush survival from batteries , it sounds like you have a regulated supply that you just need to disconnect reliably.