Raspberry Pi hat design
1) Sure. As long as there's >20mA available for each loop, they wont care what else is hanging off the same supply.

2) Sure, each loop will still only have 4-20mA flowing through it (during normal operation), so a 200Ω resistor will produce 0.8V-4.0V.

Double check that the "grounding" of the meters is correct. Be sure you have a "three-wire" 4-20mA device, and that the connections are supply, signal and ground.

3) No, for two reasons. Firstly the capacitor needs to be from signal to ground in order to filter the pulse, and secondly, the 24V needs to be reduced to interface to the Pi.

4) This is an RC circuit. Use $$V_o = V_i * e^{\frac{-t}{RC}}$$ where Vo is the voltage coming out (going to the Pi), Vi is voltage coming in (the pulse), t is time, R is the resistance and C is the capacitance. Consider all your possible Vi scenarios and see how C affects Vo. You'll probably find you'll struggle to find a satisfactory result! You might want to consider either a different debounce circuit or just doing it in software.

5) Provided you fix the pulse input, then it could be.

Generally speaking there is a lot going on here. It might be easier to get help if you focus on one problem at time.