Utilizing extra inputs - Extra IAT and MAP sensors

I'm building a 1987 Toyota MR2 and have a 4th generation 3SGTE (2.0L turbo) engine fit to the car. Currently building an engine wiring harness to match my EMU Black and an MCE18 expansion module from CAN Checked.

2nd MAP channel: At this time, I'm intending to use the internal 4bar MAP sensor on the ECU to monitor pressures within the intake manifold, via ~20" of vacuum tubing. This leaves the factory 2.7bar pressure sensor available for other uses, though I'm unsure of what to best repurpose this to monitor.

2nd IAT channel: Similar story to above, but I've the available input and a spare IAT sensor on hand. Main IAT sensor is within the intake manifold. Could mount sensor pre-turbo, post turbo before the intercooler. Which would be best to monitor?

What do you want to know? If you want to know what the exhaust pressure is, then use your pressure sensor to measure that. If you want to know the boost pressure (pre-throttle) as well as the manifold pressure (post throttle), then mount it there.

Same with additional Air temp -- want to know Ambient Temp, or intercooler efficiency (mount ahead of intercooler) -- mount in the appropriate spot.

As David suggested, only you can make the cll about what else to monitor.

Depending on how it's fitted, might be worth fabricating/fitting tapping points where you can fit it to monitor those points, and plug when not in use.

It may not have the range for exhaust manifold/pre-turbo' but if you do try it, use some pipe/tubing to move the sensor from the heat.