This all seems like truly sensible and professional advice, but is perhaps overly cautious. I'm still deciding, but the professors I've spoken with have uniformly said that it's more important that you think deeply and consider all your options than rush to let places know. I'm sure the DGS might get a little butthurt when you decline, but everyone else is going to understand (and in fact expect) that you need to go to the best school for you.