local currency

None. Use your ATM card to get Euros from a bank ATM.

And you will find credit cards widely accepted.

We got $100 worth of Euros for a 13 day trip. We had to work to spend it before we left.

Since I travel with multiple credit cards and multiple debit cards as back-up, I always have some euros on me as well for back-up. I usually figure on having about 50 euro in small bills per person. May not need it, but nice for buying water or snacks for a few euro, and I have needed cash for parking and laundry.

I doubt you will find cash-only restaurants and stores in Ireland, but not unheard of in some places.

You won't need much cash- if you do decide to get some out in advance just remember there are two currencies on the island depending on what side of the border you'll be on (euros in the Republic and GBP in NI).

Although I use credit card or Apple Pay for most purchases, I like to have the equivalent of $20USD for just in case situations. Examples of needing cash, self service laundromats and Honesty Boxes for a sweet treat.

I needed coins for the bus in Dublin (2 EUR for each trip). I also needed cash (20 EUR) to pay for a concert at a church in Dingle. I don’t recall needing cash anywhere else.

I’d probably take about 40 EUR from an ATM.

You need cash to tip guides, house keeping staff, etc.

Also note that, if you venture north into Northern Ireland, the currency is the British pound. As others noted, it’s good to have a small amount of cash, as a few smaller restaurants, etc. still resist credit cards or tap and pay.

My philosophy is that if I have euros left at the end of a trip, it's a sign that a return to Europe is in order!
We will need euro to pay for our trap/pony ride on Inishmore. But credit cards are our usual method of payment.
Beware when using a cc that you do not accept the offer to pay in USD because the exchange rate will not be to your advantage! And be sure that the cc you use does not charge a foreign transaction fee.