Having a dedicated card/account for just paypal is easier.
I highly recommend that instead of Paypal too if you suspect a site will have a much higher chance you'll need to reverse a charge. Paypal has longer wait times for disputes than the CC companies. CC companies will also have your back a bit more, typically.
[1]: https://www.paypal.com/us/smarthelp/article/where-can-i-find...
It used to be completely rediculous how much PayPal would charge for conversion at the time of a transaction, but recently (I think in response to a lawsuit) it is only somewhat unreasonable (probably the 4% you mention). You can still get a better rate if you have funds in PayPal and do the conversion first and pay in the correct currency. However, then you risk a lengthy pain if PayPal decides to close your account randomly or block your access to it.