How much cash do I need take from ATM for Greece trip?

Most places take cash. I tend to use cash a bit more frequent than the credit card. I probably use the credit card for purchases over 25, maybe 30 euro. I just find it easier to use cash. Not sure what you mean by "how much cash from the ATM." You take want you need.

Need? There is a chance you will run across a cash only place, so carrying 20 or 30 euro in small bills isn't a bad idea. Doesn't hurt.

Have a little cash like Mr E says is a good idea.
I was in Greece, mostly the Peloponnese area for 4 weeks and only once did I use cash . And that was for a total of 5 euros for 2 teas. Otherwise everywhere even in small grocery stores for small purchases, I used a credit card and not one negative vibe. For me it is much easier than dealing with cash. But everyone is different

The Greek government has now made it mandatory for all businesses to accept credit cards but you'll find many businesses that prefer cash. It's a way to avoid paying taxes as cash leaves no paper trail.

It's up to you to decide how you want to pay.

I usually pay for higher price items like accommodations and car rental with credit cards and the rest in cash.

Their may be a limit from your bank as to how much you can withdraw but you usually can take out at least 400 euros from ATMs.

Make sure you know exactly what's involved with ATMs in Greece so you don't get over charged with superfluous fees.

We got some negative vibes in restaurants in Crete in September when we pulled out a credit card. Nobody refused it, but we started using cash for meals & everyone seemed happier. Someone mentioned the credit card company fees had increased.

We did use our card to pay for hotels and excursions with no issues.

As I stated in my post cash is preferred because the business can get away without paying taxes on it since there is no "paper trail" with cash.

If someone gives you the evil eye about using a credit card tell them you have no cash just a credit card, especially after you've eaten a meal or want to buy souvenirs or gifts.

Bring cash -Euros, not dollars. Get them in advance at your local bank and get small bills, €5, 10 and 20's.
You'll need cash (and some coin) to pay a tip to your guides, to buy trinkets, bottled water and gelato or baklava for items under €5, some bathrooms you may need to pay 0.50 cents. And if you leave tips for your waiters, we usually leave €1 or €2 coins on the table as we couldn't add it to the credit card bill. We also encountered some churches where the admission was €3 or less and they wanted cash and did not have a credit card machine. We also used coins to turn on the lights in churches, pay for a lit candle, etc. We also had euros in cash just in case we got the taxi driver who said their credit card machine wasn't working.
I'd get €100 for your time in Italy and Greece.

We got some negative vibes in restaurants in Crete in September when we pulled out a credit card. Nobody refused it, but we started using cash for meals & everyone seemed happier.

Yes, because they want to avoid paying tax, a massive problem in Greece (to the tune of around €65bn annually) and one that contributed to the crisis in 2009 and saw them being bailed out by other European countries. Don't allow yourself to be intimidated into paying cash, establishments have to take card payments by law and as a customer you pay however you want to pay.

There is one way that you can pay ethically by cash and not contribute to tax-avoidance. If when the bill is presented, you ask for a printed cash-register bill (not a hand-scriibbled one), then you know that the cash receipts will be recorded in the register and count toward the restaurants' income for tax purposes. When I'm in small family-run tavernas in Greece, I know they don't have a big profit margin, and the credit-cards charge them 5% for usage, so I try to do this & save them the 5%. Most tourists are thoughtless about this, and only think of what's most convenient for them.

establishments have to take card payments by law

Really? That's amazing?