I have already calculated some things. May be they are interesting:

I do not need RMS chip, because:

efective values:
. . . . . . . _
Ieff =I/(/2)

. . . . . . . . ._
Veff =V/(/2)


So, effective power will be:

P=(I*V)/2

You need just divide product by 2 :)
Phase shift is automaticly calculated, and result will be in [W].

Scond thing. If curency is max 10 ampers, to get 5V difference can be used 0.5 oms rezistor:

R=U/I=5V/10A=0.5 Oms

Power loss in rezistor per 30 days:

Q=U*I*t=~46kWh

0.15% precission can be achieved using 8 bit A/D converters.

So, that is good enought for my needs at the moment :)

Thank you for help :)