"The thing is, I have no practical experience with industrial equipment and I would rather not make mistakes that could have been avoided."

The most common mistake is to believe that 4-20 is 4-20.
make room for adjustment.

"if You want to do a good job you use a 100 Ohm resistor followed by a opamp stage"

4-20 is designed to handle multiple units in series, and there is a definite limit to the available voltage a unit in the loop may drop. Make your resistor as small as you can. (100 ohms *20mA is 2V which is reasonable), the 250 ohms suggested will throw some units off. Also remember YOU CAN NOT ASSUME GROUND, allow both ends of your sensing resistor to float between +- 24 or more volts. If you use a +-15V supply op-amp, proper selection of resistors accomplish this easily. A small capacitor across your feedback ressistor will allow you to suppress some noise without affecting other units in the 4-20 loop.

4-20 is a son of a female dog, but properly handled (obedience training) can be processed quite well.

General for industrial equipment, take many sample and use the average, this is the most efficient noise suppression you can achieve.

Have fun,

Erik