Marina options are:
Southside -
Poolbeg YC - Private marina, but they take visitors. Closest to Dublin but in a commercial harbour area adjacent to a busy road. Walkable to Dublin City Centre however.
Poolbeg Yacht, Boat Club & Marina : Overview
Dun Laoghaire Marina - Large organized commercial marina. Excellent transport links via train and commuter bus, its maybe 25min on a DART train into Dublin city. Nice area with local pubs, restaurants and hotels.
Greystones Marina - Further out but on a less frequent DART service, maybe 45min to Dublin. Large organized commercial marina. Lovely village!
A midpoint between these two is Dalkey - where Bono lives - which is another lovely village but the harbour Dries and isn't secure. The coastline from Dalkey to Dun Laoghaire is nice.
Fuel - Not sure about petrol availability in these marinas. Diesel no probs.
Northside:
Howth Marina - Private Marina that takes visitors. Nice clubhouse with bar. Nice fishing village. Nearest hotel is 1.5km away but there are B&B's and a friend has a nice Airbnb that I would recommend. Nice hillwalking options and loads of Pubs. There is petrol available in the Club via jerry can but it is pricey. DART takes 30min into Dublin. I must like it 'cause I live there. Has the best cruising area in Dublin imo. around howth head and islands to the North.
www.hyc.ie
Malahide - Large commercial Marina. Petrol available. Lovely village, lots of pubs and 30min DART trip to Dublin. Hotel in village.
Malahide Marina - Malahide Marina