Dual 0-5V analog inputs and one 0-5V analog output - Best approach to take?

I am new to Arduino and the choices are bewildering. I'd appreciate guidance in selecting the best hardware solution for my project. My project is to create a fuel totalizer for an amateur-built one-man helicopter. I want to input 0-5 volt values from two capacitance fuel probes that are measuring fuel levels in two irregularly shaped tanks, then using look-up tables to account for the irregular shape of the tanks, convert the raw values to fuel quantity in each tank, combine the two, convert back to 0-5 VDC and drive an analog fuel quantity indicator. The indicator has a 270-degree sweep, so to make it read smoothly I would like at least 9 digits of precision, although 8 might work. Speed is not an issue so I could multiplex the two inputs to a single ADC. To avoid EMI problems differential inputs would be necessary. All help would be much appreciated!

The ATMega chips the classic Arduinos are based on all have an ADC with 10 bits resolution and a reasonable degree of precision and accuracy. They also have a built-in 4 (or more) channel analogue switch, so you can easily handle tasks requiring 2 or more channels and sampling rates up to a few KHz. The ADC and analogue comparator can be referenced up to the value of Vcc (usually 5V) with no trouble.

Inputs are single-ended though. You'd have to make up your own differential front-end.

The ATMega doesn't have a DAC, but it does have good support for pulse-width modulated digital outputs. These can but run through a low-pass filter with a cutoff of 0.5 Hz or thereabouts and could go into a moving coil meter just fine.

Would it be possible to add something like the MCP4725 12-bit DAC and the ADS1115 ADC from Adafruit using a daughter board? That looks like it might give me the differential I/O I'm looking for.

Do you mean this --> Overview | MCP4725 12-Bit DAC Tutorial | Adafruit Learning System

Yes. That looked like an inexpensive way to get me the 0-5 volt output I need with enough resolution to satisfy my needs. But how do you interface to the processor without using a proto-board and jumpers? I want to make a circuit that I can actually use in my helicopter and not just play with on the bench.