Sandyford would be deadly.
TBH I'd pick any location carefully, you don't really want to have a homebrew shop associated with cheap nasty booze - certain areas of the city/suburbs would tend to attract more people who are just interested in cheap nasty booze than craft beer.
Just saying.
How about getting a concession type thing in somewhere like stephens green shopping centre or powerscourt centre maybe - dunno what sort of money you're talking though. How about the organic market in temple bar - would just be a saturday, you'd need to travel to it, but would be a lower overhead I think than a fixed shop with staff, but little footfall week-round.