using high and low switch together on a load
the Q2 transistor was getting really hot.


Because the collector was held at roughly 11 V by the b-e junction of Q1, and nothing was limiting the current from 12 V, through the Q1 b-e junction, to the collector of Q2.

You can add another resistor (or simply move R1) between the collector of Q2 and the base of Q1 to limit Q1's base current and reduce the power consumed by Q2.


  how can I calculate the resistance value for R1, R2 , R3?


You want to allow enough base current for the transistors to be fully saturated. That means about 1/20 to 1/10 of the collector current.  

The collector current should be limited by the circuit attached to the collector, which your circuit doesn't do, unless your LED strip provides a current limiting mechanism. If not, you can add a resistor in series with your LEDs to limit the current through the Q1 and Q3 collectors.


  what are the power rating should I be using?


Once you've finalized your circuit, figure out how much power each transistor will be consuming, and use a rating at least 2 or 3x that value.