How to design the stop button?

I'm using Mitsubishi FX2N. There are so many situations that we should trigger stop for whole equipment. For example. a sensor hasn't sent the signal to input contact for long times. Should I use stop button to trigger an internal contact, like X10 to M20, then use the M20 inside my plc program?I think M20 is more flexible for different situations, like "stop now" or "stop after 30 seconds".

As a rule I like to check an input once, or if a combination of inputs is used more than once, and set an internal contact like you thought of.

I find it easier to program and make changes in the future.

This looks like a design pattern
I also combined some instructions to an internal contact, like M70 to RST C2 and RST M80 so I can use M70 when I need to reset them.Then I run into a trouble: I used to think from input to output to write the ladders, now because of the error about "double assignment of relays or outputs" occurs, I need to reconsider a lot.

When I'm programming, I always have two functions. One is at beginning and I call fbIndirectInputs, and other one is at end and I call fbIndirectOutputs. I use fbIndirectInputs for forwarding all digital inputs (X) to adequate M addresses and fbIndirectOutputs for forwarding relevant M addresses to digital outputs (Y). In fbIndirectOutputs i have on input side also two additional inputs I call "mEmergencyStop" and "mPause", so I can easily define what to do with outputs in case of emergency stop or in case when there is need to pause the process.