Grand area. There's no real issue with traffic leaving Mt Argus to join the Lwr Kimmage Rd as there never seems to be too many coming out at once. Lwr Kimmage Rd itself can be slow going from 7.45 onwards
I walk through the Church Grounds regular and have never noticed any issues. You can also go to the Bus stop via the park itself, closer to Sundrive Junction so as to avoid walking through the Church grounds.
There's occasional drinking going on in the park especially during the Summer...you see the bottles left around the park benches. Young lads and lassies mainly.
Supervalu is indeed the closes supermarket. After that it's a drive to Rathmines, Ashleaf, Crumlin Rd shopping Centre or Terenure.