1. There are many choices when it comes to WDW, but no wrong choices!(except maybe staying offsite or not having a at least one Mickey bar while you're there.
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2. Begin with a budget. You've already decided on driving and onsite, so that is two big choices done.
3. Limit your trip to WDW property.
4. Food. Although there are variations in food costs, it's easy to set a baseline by looking at a few menus. (use WDWinfo.com) Compared to eating at home, eating at WDW is expensive, BUT compared to my experiences at other amusement parks, you get pretty good quality for what you spend. One easy option is using a package and the
Disney Dining Plan. You'll get some savings off your meals, you'll get a mix of table service and quick meals, and you'll have everything prepaid. It's very relaxing, and your guest will be able to pick what he wants from the menu without regard to menu price. The only thing you'll have to spend oop, is a few small things here and there, and meal tips. I don't suggest either the QS or deluxe meal plans. (one has minimal benefit, the other too much food.)
5. Resort. Use WDW's website to
see the options. Do not book via webpage, call. You get better terms. Look first at what's available with the discounts they are currently offering. (you have to look click on "special offers") Don't worry much about trying to find the best pool or other details...look at what appeals to you, what's in your budget, and most importantly what's available!
The end of March is a fairly busy and fairly expensive time to go, but that's because it's also one of the best times to go in terms of weather.
7. Length. It sounds like you have a length in mind. I suggest six full days as a good baseline. If you can afford more or less that's fine, but six is a good baseline. It gives you one full day for AK/HS, and two full days at MK and Epcot. That way you get to see mostly everything and get to keep a busy, but still doable pace.
8. Park tickets. I'd keep your park tickets basic. You might consider hopping, but you won't really need it. (You can use it to hop into a different park at night to take advantage of extended hours, but only if you'll still be up for that much going.) That's the only added feature I'd consider for this trip.
9. Begin booking, ASAP. CAll to book your resort first, then add dining.
As far as resorts, if you can afford a deluxe, you'll probably appreciate the convenience they offer in terms of location. You'll also feel slightly more taken care of at the deluxes. Of those, I'd suggest BC/YC/BWK. More pricey is the Poly, less expensive but still very nice is AKL or WL. Teh DVC rooms will give you more room and a kitchen , but they can be pricey for what youare getting. Two regular rooms might be a better option.
If that's not in your budget, the next choice would be a moderate. POFQ is compact, but all are nice. At the mods, you'll get a fridge in your room and a coffee maker. the others are large, but I really llike CSR. CBR is less streamlined, but the boys would probably LOVE the theming. POR has an extra murphy bed, but we liked it least of the mods. (The buildings in that part of POR have no elevators. If you stay there, request a first floor room!)
The values are also nice and clean, but they do have less amenities. You'll still get many onsite benefits, and the price is quite a bit lower. It sounds like you'll probale need two rooms, so this may well be a great option.
I've never stayed at FT. Wilderness, but given your party size, it might be a great option.
10. More: if you don't opt for a meal plan, then you'll probably eat mostly all QS, but then you won't have to pick any dining ahead of time. You have total freedom to eat when you want. The disadvantage of the meal plan, is that you'll need to select some dining. I'd eat breakfast mostly at your home resort's food court - or - eat alight breakfast in the room each day. I'd eat QS lunches and use the TS for dinner.
As far as dining choices there are many and no wrong ones. Use the dining finder to pick choices based on what kinds of food you like or are willing to try. If you are staying deluxe, I'd plan one dinner at your home resort, and a second one at a neighboring deluxe resort. (then you can go tothe room easily before or after dinner). At a mod you can also dine TS. I'd pick at least one character meal, try any meal at Crystal Palace in MK if you can get a table there this late. (Again, you'll be a little limited by what's available at this point, but that's okay.) If you find your dinner options aren't wide, try TS lunch availability. Honestly, we find at WDW we are easily able to eat at odd times. The only choice that doesn't work especially well is eating dinner VERY late or breakfast very early (though others love it). Eating an early dinner, late breakfast is no problem, since you can skip a meal that way.
I'd also keep your trip basic in terms of not trying to do tours, water parks, offsite parks.
11. Touring tips: Try to use the extreme park hours as much as you can. Try to start your days at the parks at 9am, and be in parks late at night. That is when crowds are lowest. Taking afternoon breaks is good if you can't go all day. But if you don't make it to every rope drop or stay until close every night, that's fine too, you'll just get bigger crowds. Use Fastpass for the big rides.
12. DO bring a double stroller for the little ones! Plus the stroller will give you a means to carry water. Do minimize what you bring to carry all day! but do bring alng bottled water and DRINK IT! Also try to drink water with every meal. Do encourage the kids to eat fresh fruit and vegetables sometimes. Do encourage the kdis to eat yogurt, if they will. All of the above eating tips will help prevent illness. Do bring moleskin. Do insist on two sets of walking shoes for everyone!
and help me out!! PLEASE!! 
It's not a sofabed, but a Murphy bed that folds down from the wall in the living room. Sorry. Much more comfortable than a sofabed, btw. (I'm surprised no one caught my mistake!)
What great suggestions. I just thought I would at to his/her #12 point.
