I live in Malahide and I probably would never make it to sandyford - driving to blanch/M50 on a saturday is torture.
If I were you setting up a shop like that in Dublin, I'd pick an area central - eg - look at the dublin bikes zone - I'd agree with the previous comment about not going south beyond the canal.
If you go north / south / west - you are bound to become unattractive to distant customers
Just my opinion - best of luck !