If at all possible, you will want to avoid the DC area around rush hour, especially the mixing bowl/area just south of the mixing bowl where the lanes merge. If you don't have one, DO strongly consider getting a toll transponder. Know the carpool rules. Do consider using toll lanes in VA and FL. Florida now has a lot of automatic toll lanes, so it is a good idea of have a transponder when driving in FL.
There are a number of spots along the way that make for good places to stop! It depends a little if you are talking about just an overnight stay/get back on the road, or you are talking about spending half-a-day somewhere.
If you don't want to commit ahead of time, you can very much find a roadside hotel based on how you feel that day. You can also do a little research and sees what appeals to you. ALWAYS though, do not walk in the lobby to book your hotel. CALL or book AHEAD via internet/phone. Via internet/phone you can search the best rate and good reviews. If you are going with Hiltons, I suggest the Hilton website. Marriott is another option.
One possibility, weather permitting, there are many nice beaches to consider all along the East Coast.
DO NOT SPEED in Virgina. We should all obey traffic laws, but VA has hefty fines with a history of speed traps that LOVE to catch out of state plates. The state also uses speed/red light cameras if you get off the highway.
Raleigh is a little bit out of your way, but it is a nice area. Charleston is also pretty nice, but also slightly out of your way. Savannah is right on the way, and an interesting stop.
There is a GREAT Fairfield Inn in Santee,SC. There isn't a ton in the area, but you can get great food, including fish from the lake. That area is also home to low country cuisine.
If you stop in Savannah: There are some inexpensive hotels (breakfast included- either Marriott or Hilton brands) near highway. If you want a place with more atmosphere, the JW Savannah Plant Riverside is spectacular! The Alida (also Marriott) is just next door, also very nice, and very walkable to the lobby of the JW Marriott if the JW is too $$$. The JW is along the river, and the riverwalk is really neat, with plenty of places to eat. You can go there just to visit, too. If you walk beyond the Marriott's riverwalk, there's more places to eat all along the river. A good option is the Boars Head. Also a fun stop is the SCADstory. I think you have to reserve it, and they request small donation, but it is a neat way to learn about SCAD college. The college has done much to transform the city. The SCADstory is a somewhat Disney-esque immersive experience about the college.
IF you don't have AAA, consider getting it. If nothing else, you can re-coup the cost in hotel savings.
DO stop at the Georgia visitor's center on I-95 at the GA border! Very clean, restrooms, quick stop to get GA information.
If you don't want fast food, you can find other option using your phone. One kinda fun option is BBQ, if you like either NC or SC style BBQ.
There isn't a ton in Brunswick, but it has inexpensive places to eat, as I recall. It has been a few years. You might consider Jekyll Island or Tybee Island. Jekyll Island has multiple nice hotels.
Charleston is slightly out of your way, but also a nice place to stop. There too, you could choose a roadside hotel like a Hampton Inn and just venture to the city to eat/explore.
Jacksonville, FL also gets busy at rush hour. For that matter, Orlando is also a pain at rush hour.
There is tons of fun stuff and history in St. Augustine. (about 2hours from WDW) There are lots of places to stay, either along the highway, in the city, or out by the beach. The fort (Castillo de San Marco) and surrounding area are a place everyone should see! City is very pretty/historic, and there is a long area of shops to walk around. There's also the Gator Farm- a Florida sightseeing classic!
If you stay along I-95, Daytona is another option to stop, but by then you are only about an hour from Orlando. There are also a LOT of beaches all along the FL coast.
One thing that might impact your travels in Sept is the weather. You'll want to avoid big storms of course, but also know you might encounter sudden downburst rains/lightning storms in the south. The rain is often VERY heavy to the point of white-out. Storms tend to occur in the afternoon. They are also often short-lived.
You will probably take I-95 to I-4, but if you are willing to go about 50min detour, coming down through Ocala NF is a neat option.
At WDW, the guard will ask if you have a reservation, your name and to see your driver's license. Usually your last name suffices for them to find your reservation, but not a bad idea to have your reservation # handy. It is probably also helpful to do the online check-in. First time through, you have to talk to the guard. After that, you can scan a Magicband to enter via the automatic gate (usually to the right.) If you don't have a Magicband, then ask about other options. I think there are other options, but I'm not sure (phone? scannable card?).
