I need to know that the cedar siding should be primed and painted before installation on both sides or primed and painted after installation just on exterior side ( only one side that is exposed to weather). Thanks

You should prime all sides of the siding panels even any cut ends during installation. After the sidng is installed you can then have it painted the desired color.
If you decide to stain the siding, again, stain all sides and the cut ends.

Don't paint it, stain it! Let the natural wood grain show through. Use a transparent stain of good quaility and high solids such as Cabots. Stain the cut ends prior to installation.