Kind of interesting that you live in a state with four seasons, therefore, some cold temperatures, but followed the manual on the coolant. Not every Explorer is the same, but this tells me that changing of the coolant more than required, related to its effect on the water pump, may not be all that necessary except for peace of mind or certain driving conditions. I'm complete agreement with you in regard to changing out the water pump at around 100k to 130k miles as preventative maintenance based on the potentially catastrophic design. Most cars with timing belts require the belt be replaced at around 90k miles or within a certain time period which is usually reason to replace the water pump and pulleys, hence the reason they sell timing belt kits. Also noticed you changed your transmission fluid 50k miles of ahead it be required which makes sense.