As far as finances are concerned, you get quite some help from KI and then there is your CSN. I had some savings from before as I like to spend a bit on travelling and food. But, be assured that the 12000kr you get from the Erasmus program and your CSN will be enough to survive as Dublin is cheaper than Stockholm for many things such as food, groceries, drinks etc. For myself, I required to get a visa for Ireland so that added to the costs a bit (If there is anyone that requires information regarding this matter you can contact me separately as most people don't require one). You can join the societies you like for a nominal fee and if you join classes then you have to pay per class (like painting/pottery/photography).
For basics such as groceries, you have several options for example TESCO, which is one of the cheapest.
A mobile connection there is also very convenient, you can buy a sim card and top it up with 20 euros (most companies) every month for free calls and unlimited data.
Transportation is a bit expensive in Dublin actually for which the best option is to walk or bike. I used to usually walk unto most places but also its good to get the Leap Card which you can get at Trinity College (where they sell the Student Leap Card, which is cheaper) during the first few orientation days. The Leap Card is valid on buses and LUAS (their trams system). You have to keep topping up the card and can even use the app which is linked to your card.
You can use your bank card from Sweden very easily in order to take out cash or pay with the card in almost all places.