For me, it would be so stressful. And it's really only because of the logistics. Even something as simple as getting the older two to the bathroom and not leaving the baby unattended.
I either take the stroller into the bathroom with me (if I have to go) and use the big handicap stalls at the ends. I have two huge doubles, one Graco duoglider and one side by side and they both fit fine. The older two go, and then I go while baby is in stroller. If I don't have to go myself, I just hold the baby and take the other two in and pick one towards the back where I just stand there with the door open while they go. It's the same as at home, I am usually holding the baby and trying to wipe DD3! It's great fun!
Or having to have everyone stop if the baby needs to eat or be changed.
This is pretty easy. Changing doesn't take that long. I use the back seat of our stroller and lay it completely flat so we don't even have to be near a bathroom, just go out of the way so everyone isn't privy to the changing! The baby can eat while on many rides. Hop on the Railroad and feed bottle/nurse there. The olders will still have fun and you kill two birds with one stone. You can also do this on Pirates, Jungle Cruise, Small World, etc.
Coordination of naps, food, tickets,
As far as naps, for us they nap in the stroller or IF (hardly ever) we go back during the day, I try to keep the baby up or head back right when they are getting tired and we all nap! Other times I hold the baby while napping and we just go on lots of rides. Food is tricky as I said earlier, sit down places are best because it is hard with food, tray, baby and kids to balance it all and pay. Let someone wait on you and make some PS's. I hold all the tickets in a little holder and 2 kids are in the stroller as we enter the gates, and one is holding on. They will let you all go through the stroller entrance together since yours are so young!
how to get on and off rides, having to go on rides that everyone can go on and figuring out seating,
This is pretty simple really. On rides like Jungle Cruise, you all sit together. Same with Pirates, Haunted Mansion, Teacups and so on. On dark rides, the 3 year old will enter the front seat first followed by the 4 year old. Then you and baby will be behind them in the same car. We all get out at the same time, or I get out first (Pirates) and help the other kids out! There's not that many that you all can't go on as I posted before!
standing in line holding on to an 8 mo old and having to corrall the other two. Having to let go of hands to get tickets.
The only times I let go of hands is if the older two must have a hand on the stroller at all times. I make them get in it at times where I cannot hold them. Also I highly recommend a sling/carrier for the baby so both hands can be free for the other two and you don't have to take the stroller ride to ride. Just park it and do the area if they can walk it! Also my kdis know they must behave while in lines or we won't be able to go ourselves so there is no corralling. Just walk single file with them right in front of you as I am sure you do even with help!
It's certainly doable, but I'd be so stressed out the entire time I'm not sure it would be worth it.
As an alternative, could you bring a friend or even a teenager or older child with you to help out. They'd get a DL trip and you'd get a pair of extra hands.