We do CHOC Walk every year, and it's a very crowded day. Many walkers only have that one day in the parks, so they make the most of it. Definitely tell your friends to do anything they need to get done at the ticket booths the night before, if at all possible. The esplanade will be a mass of humanity for the morning while walkers get their discount tickets. They only get that one day to use their special offer for tickets, so they don't have the option to come back another time. Last year we had 14,000 walkers (and that was low because the date had been changed with relatively short notice). The year before, we had about 16,000 walkers. This year we still have the changed date but more advance notice, so no one knows yet how many people will sign up. DTD will be a mess in the morning, but should clear up by late morning/noon. Will your friends be staying on site or walking distance? Stay away from M&F until much later in the day. Walkers will fill that structure in the morning (Disney tells us to park there), and exiting the structure can take quite a while after the walk is over. The parks will be crowded all day, but it won't be any different from any other crowded day. Less than a bad day during Christmas week or HalloweenTime. Just use good planning and organization, take a break when needed, and have a positive attitude. Your friends should be fine.