I lived in Costa Rica for a year and a half and it's pretty easy to get cash from an ATM. But it's been a while, so maybe someone else has some updated info?
Definitely call your bank first for 2 reasons. 1: to make sure your ATM card is going to be usable at international ATMs (I had to get a different card) and 2: To tell them the charges are legal and valid, otherwise they may put a stop on your card when they can't contact you by phone and you are shit out of luck. Same with your credit card. It is safest to tell them you are going first.
Where are you staying? San Jose or out in the middle of nowhere? How are you getting from the airport to your hotel? A lot of places in San Jose and big tourist areas will actually accept US$, especially nice hotels and restaurants. ATM withdrawals are the fastest and cheapest way I found to exchange $ to colones for bars and whatnot.
ATMs are easy to find in San Jose, lots of international and CR banks all over. Even a few US banks there now. Out in the little beach towns you are more likely to see just Banco Nacional or BCR but they will have ATMs. Your bank may not charge you a fee, but you will probably end up paying the fee from the ATM's bank unless Schwab refunds that too which would be pretty impressive. Just like in the US, the ATMs at actual banks usually have lower fees than the ones you see at malls or tourist places and I always felt a little safer using them because of bank security guards. Skip the ones in the airport if you can, you'll pay more in fees. Also, fees should be per withdrawal as opposed to a percentage, so fewer transactions of more $ per transaction are generally cheaper. Shouldn't be too high a fee, a few bucks like here in the US. Be careful not to put the wrong pin in; a machine once ate a friend's card.
If you pay by credit card you will pay more than if you pay in cash in a lot of situations, including hotels and restaurants, because they can pass the credit card company fees onto you. That is perfectly legal and acceptable down there. It can be quite an upcharge too. Cash is generally best for small hotels, bars, cafes, shops, taxis, etc. So yes, there is a hidden catch with the Discover card beyond the foreign transaction fees. Not only that, but Visa and MC are much more prevalent than Discover in my experience. For big hotels or a tourist package you are probably fine with paying by CC.
Have a back up plan, like carry the debit and credit in 2 different places, leave debit behind once you've gotten money, have US $, etc. I once got pick-pocketed in San Jose and my debit card was stolen along with most of my meager available cash. I had a credit card back at my house, but I used the VISA to get an emergency cash advance and boy did I pay for that mistake. If you have some US cash, you can exchange it at a bank for a reasonable rate or just use it as is.
Have a great trip!