reading rpm gauge and pressure sensor

Hello,

Trying to use an arduino mega to ultimately control small diesel engine that is used for irrigation remotely.

So far have gotten the arduino online with an Ethernet shield and also have the relay's working that would be used to rev up and down the motor.

first of i would like to see the pressure that is going out of the pump.
Looking at a big variety of pressure transistors online. Found one that seems to work for my needs and it allows with ordering a selection of output signals.
What would be easiest for me to use so I can read the output without needing to add additional parts?

Options are 4-20 mA, 1-5 vdc or 0.5-4.5 vdc

Pressure sensor is 0-300 psi but reading through forum and other tutorials I seen people either using voltage devider/splitter to lower voltage as it seemed it can't read full 5 volts or bring up the mA as it seemed it was to low for it to read either.

Second the rpm gauge. It has three poles on the back +/-/s the plus and minus are 14.5 dc volts when its running the s is what gives us the rpm readings but I has me stumped a bit. With my voltage meter I got 4 ac volts.

Using neighbors klein cl1000 meter I could read hertz as the document for gauge was show 2.5hz to 25khz. Taking a reading from idle to full throttle I got 1.1khz to 2.2khz at 49.8 duty cycle. but it also showed a range of 20 to 25 volts input.

What would be the best way to read the input going to the gauge and also protect the arduino?
Seen some voltage splitters that just used two resistors and others with additional components.
is it best to try to reduce voltage and read that or read the hertz but somehow isolate the higher voltage.
Does a voltage splitter change the hertz or only take out the voltage?

Some direction would be appreciated have some electrical knowledge but very minimal electronic.
Was hoping to use the link below to read the frequency but concerned about frying the board.

https://tushev.org/articles/arduino/9/measuring-frequency-with-arduino

Thanks

I would get the 0.5 to 4.5V pressure sensor, can you post a link to the RPM gauge?

Attached link below regarding the gauge, didn't find exact model number or anything on it but just dug around online with the name in the gauge to find something that looked the same.

Link to rpm gauge of producer

Link to a seller that has a working link to a data sheet that I found.
https://www.dieselpartsdirect.com/athi40a