Got the wrong aftermarket gauges? Best answer is replace the sensors with ones that match the new gauges, there is less to go wrong in some expensive ways that way. Just so you later on don't say no one told you so.
You're not reading ohms through analog in and you're not outputting ohms through analog out. You can read volts if you wire the circuit up right and you can output pulsed power.
Have you look at the analogRead() example to see how it's wired? Sensor to analog pin through resistor, yes, same sensor to ground through a much bigger resistor (10x or more) is what I see works.
Step 4. I have a value from analogRead(), I've scaled it and now I need a value to feed analogWrite()... what should I do? BTW, analogWrite() uses 0-255.
Start out with simple things like hey, read the sensor and see if the data meets your expectations. Check every step before you try to put them together and expect every step to take 3x or more time than you thought it would. If you do enough simple things then you will learn some electronics along the way but be sure to do extra reading and start off with Ohm's Law.