We are flying in on Wednesday around 1:30pm and will be leaving Monday morning around 8am for Lake Tahoe.
Most of the water in Guadalajara is NOT potable, meaning you can't drink it from the tap. There is bottled water literally everywhere. You cannot walk far without finding a little store or gas station to buy some, and it's cheap. I recommend buying a few big bottles at the gas stations (called OXXO's) to have on hand because the Hyatt will definitely be more expensive. The hotel replaces your bottled water daily (It was about $2.50 each if I remember correctly...). That being, said I drank water from the hotel tap the entire time at Javi's sister's wedding and was fine. I stuck to bottled water when out and about or eating in a restaurant.
I ordered a bunch from my bank (Bank of America) and they mailed them right to my door a few days later. Most places around the hotel accept credit cards. There is an ATM right in the lobby of the Hyatt but it charges you about 3 bucks every time you use it.
A lot of places accept credit cards but I would bring around 2,500 MXN (definitely more if you want ball out on souvenirs) for each person coming. Save your cash for tips, souvenirs and artisan items and use credit cards for everything else. To give you an idea of how much things cost- a margarita with top shelf tequila is about $12 or 240MXN, a traditional Mexican breakfast (at a restaurant) is about $4 or 80MXN, dinner will run you about 200MXN ($10). The hotel charges $17 (340MX) for their breakfast buffet. Ask for some small bills if you can!