Because this project will require considerably more IO ports that any micro-controller can provide, I identified the best IO expansion candidate as the MCP3008. It is a $4 16pin dip ADC with 8ch@10bits over SPI interface. Since SPI can be daisy chained and only requires 4 IO pins, perhaps 2 of them will serve all the analog interface needs.

Application

16ch total = 4ch EGT, 4ch cht, 1ch oil pressure, 1ch oil temp, 1ch fuel psi, 1ch fuel gph, 1ch manifold psi, 1ch air temp, 1ch humidty, 1ch air psi

Code for proof of concept I tested http://www.hertaville.com/interfacing-an-spi-adc-mcp3008-chip-to-the-raspberry-pi-using-c.html

Resources:

http://ww1.microchip.com/downloads/en/DeviceDoc/21295d.pdf

www.microchip.com/wwwproducts/en/en010530

https://learn.adafruit.com/raspberry-pi-analog-to-digital-converters