I know you mentioned CSS, but did you check the prices at AK-Builder? He has these parts too.
When I did mine I cut the square out for the pistol grip nut, but if you feel uncomfortable doing that the rivet on one will be just as good.
But yes, get the trigger guard & selector stop that everyone has listed as the "S12" one, it's designed after the one the Russians use.
As for stock, give some more details about what style(s) you like, or if you want to mod the original mount. Anything that fits a standard AK stamped receiver will work with the S12 without modding the stock tang.