Yes, OV Pay will work with foreign bank and credit cards if they are contactless.

 

https://ovpay.nl/en/frequently-asked-questions#what-payment-methods-can-i-use-to-check-in-and-out

The conversion from euro to zloty will work like paying in a shop or a restaurant.

How many transactions will there be on the bank account? If you make 2 trips on the same day, will there be 4 transactions (checkin, refund, checkin, refund)? Or 2 (trip 1, trip 2)? Or 1 (trip 1+2, at the end of the day)?

As banks can charge an extra fee for foreign currency transactions, and the exchange rate differs between buying and selling, these fees can have a significant impact on the price of your journey and it would be good to know up front how this is going to work out.

There should be 1 transaction per day you used your card on for travel.