What sensors should you have on standalone ?

To make the best standalone ECU with all the sensors and so on , what sensors should you have to be as safe as possible ?

- EGT / 1 per cylinder

-Intake temp before and after intercooler

-Watertemp from cylinder head ( should you use more watertemp sensors from some where else ) for example , close to thermostat or radiator ?

-Oiltemp from oilsump/plug ( more oiltemp sensors from more places ?

-Fuelpressure sensor ( Maybe fueltempsensor , where should you connect that sensor ?)

-Wideband lamb , one to ECU and one to a gauge in the car maybe ? )

Extras

Temp sensor on gearbox and rear axel ?

Water temp is a sensitive thing , where should you connect extra temp senosrs for what to be 100% sure so you can catch if something is wrong ? Like if you get a broken thermostat then you should be able mounte some extra tempsenors to catch that ,, correct ? )

The extra sensors is to be able to read the car completly when mapping for example.

Measure/sensor back pressure in the exhaust/downpipe ?

Just to add on more what you think is needed if you want to go ALL the way for measurments ?

You need to look at the vehicle system as a whole. First, if I were also fitting a separate dash or dash/logger, I would decide how much information I could get over the ECU communication link. I would then make sure I was putting as many sensors on the ECU as the protocol supports. Keep them tied to the engine & transmission, though -- unless your ECU is going to implement wheelie control, there is no need for a front suspension sensor to go to the ECU :)

I think having all the relevant temps and pressures on the ECU makes the most sense. Also, wheel speed data to the ECU allows gear detection (and thus possibily gear-dependent tuning, as well as launch control and traction control. Usually you will need a clutch input for launch control. If you have a sequential gearbox and want to implement shift-without-lift you will need to have a force sensor on the gear lever.

Wideband data certainly needs to go to the ECU. It's not possible to offer closed loop fueling without it. And tuning with the lambda on the same window in the tuning software is a real plus.

Data logging answers questions -- whether you need all the sensors you mention depends on what questions you have.