Use a separate resistive divider for each Line
then you can decrease applied input voltage in range of allowed ADC input,
If your AD808 is fixed and can't be changed,certainly the resolution is 380/256=1.484(v)
you sweep entire range but not at 1 volt resolution
So for each step increas/decreas you must consider the voltage has increased/decreased 1.484(v)
About frequancy you must detect 2 zero cross of mains
you can use one channel of ad808 or use a simple opamp
circuit for zero cross detection,
Any way assume this time is 0.098 second
So T= 2 * 0.0098 = 0.0196 (s)
F = 1/0.0196 = 51.02 (Hz)
I don't have any idea about ampere detection!
About water temperature you must insulate your sensor's legs,Some temp sensors that i suggest you are lm335,lm35,lm75,smt160 and pt100
smt160 and lm75 are digital,first pwm output and another IIC serial interface
About speed of motor ,thing that is very important
is finding a method to events MCU at each round
it all depends in motor architecture and mechanical limitations
Assume it event motor at 0.018 second
so speed = (1/0.018)*60=3333.33(RPM)
You can use 10 or 12 bit adc for having better
resolution,AD7890 is one that is serial interface and
have master and slave mode
I Hope this helps,
Mehdi