If you're arriving from the United States then no need for any change of currency. Ecuador currency is the US dollar! Ecuador adopted the US dollar as its legal tender in January 2000. Also, your credit card will work just fine and there are plenty of ATMs. When using credit card, you won’t have to worry about currency exchange, but there may still be a foreign transaction fee (if you have, use a card that offers no transaction fees).
Yes, although Ecuador uses the US dollar, a passport is still required for legal entry. Note that you MUST have at least 6 months of validity remaining on your passport to enter Ecuador, if not you are at risk to being denied entry...so please do take a look at your current passport to determine when your expiration date is and estimate how many months will be remaining by this upcoming September. If too close to call, we recommend renewing your passport (https://travel.state.gov/content/travel/en/passports/have-passport.html).
Perfect. As Quito sits 9,000 feet up in the Andes Mountains, you can expect warm/comfortable afternoon's (70 degrees Fahrenheit and brisk Fall-like mornings/evenings of 50 degrees Fahrenheit). Don't let the temperature fool you, the afternoon sun (around 12-3PM is STRONG), reaching UV indexes which can exceed 10-12 on the scale, so please pack sun screen, but we'll also be sure to keep you stocked up!