First off, I'd use Open Table to make that Raglan Road dinner reservation on your first night. For starters, it's a real reservation, not an ADR, so you might be seated more promptly. Secondly, because it is made directly through the restaurant and not through Disney, there is no associated $10 guarantee. If you don't make an ADR, you are charged $10 per person. If you miss an Open Table reservation, no big deal. I recommend this simply because it's your arrival day. If your airline messes you up, you miss a flight/connection, someone is travel sick, etc., it won't matter if you miss the Open Table reservation, or call to cancel. Having an ADR through Disney means you'll lose $10 per person if you are a no-show.
We've been to WDW so many times, I've lost count, but I think we have 27 trips under our belts. When I plan a trip, I look at crowd calendars first (haven't used
UT's- I use touringplans.com, kennythepirate, or the one here on the DIS) and pick my park days that way- but also take into account that we love to do late EMH at the MK. Once I pick a park, I plan our ADRs. We usually have breakfast in our room, and one TS meal a day, either lunch or dinner, depending on our plans and availability- but usually it's a dinner TS meal.
I know that we are not morning people, so morning EMHs (as well as rope-drop) are never part of our plans. We try to be on a bus by 10am, stay all day and into the night, remembering to take frequent breaks in the afternoon heat. If MK is open until midnight or later, we might not go into the park until around noon, and we plan a sleep-in morning for the next day. Taking a break back at the room is a HUGE time-eater, and at WDW, time=money!
I consider myself experienced in visiting WDW, but FP+ and ADRs have changed my game plan a little bit. When planning our last trip, I set up my park schedule at touringplans.com. I told them which park, what we wanted to see, balanced walking and waiting, and let them give me a schedule. I think moved things around so we toured in a logical rotation, booking the FP+ that they recommended. It worked very well for us at HS, and I think we saw everything we wanted and more. We had park hopper tickets for that trip, so it was nice that we were at HS on an evening EMH day; we started our day by arriving at HS at 10:30, left after a 6pm FP+ (fourth of the day) at the Great Movie Ride, took the boat for dinner at Biergarten in Epcot (but could have eaten on the Boardwalk if we hadn't had hoppers, or less time), then back to DHS to see Osborne lights and for DD22 to catch a couple more rides (ToT and RnRC) during EMH- although she'd done them during the day, too. I was pleased that I'd used the touring plan. This might be helpful for you, if for nothing more than to give you some idea of how long to allow for different attractions and help you think about FP+ choices, even if you don't stick religiously to the plan (we varied a bit, day-of, but it helped me think through the whole thing).
I don't know if your kids are into characters, but if they are, it's usually worth the expense of character buffets. They will meet 4-6 characters during the hour or so that you are eating. You'll spend more time than that waiting in all the character lines, and you'll still have to plan time to eat. As I said, time=money, so for a few years, we found character meals to be money well spent.
If you find yourselves bored on the off day, take a bus to MK, then ferry to the TTC and ride the monorail to Epcot and back. It's free, and if you are staying onsite and using the bus system, your kids aren't going to get to ride the monorail. It's fun, and it'll keep them busy and feel like they are doing something "Disney" before going to HDDR that evening. I am not sure of the logistics, but you might be able to take some sort of transportation from MK to HDDR... you should look into that.
