It is a busy time of year - I would say "active" - it is a great time to go - mid to high 70's by day and high 50's by night - we love going at March break (go pretty much every year)
The transportation is generally very good - there is always a chance with any public transportation that there will be a delay or issue and these boards tend to magnify these problems beyond their usual frequency of occurence
Where the transportation gets sticky in my mind, is if you try and go between resorts or start trying to squeeze too many different destinations in one day especially if your kids get wired or tired
I would recommend moving to a moderate, saving the money (not spend it on gifts and trinkets), and then you have some funds set aside for the next time you go (your kids will probably want to go again and geez, you have to include the youngest next time -

)
With that time of year, consider getting to the parks early and with the ages of the kids, consider leaving late morning just before lunch - retreat to the hotel, have a meal, enjoy the resort (CSR has a really nice pool and POR has a nice ambience), maybe do some swimming and water activities, have a nap/reading/quite time then (assuming you have park hoppers) head out to a different destination mid-to late afternoon.
That time of year, the park hours will be extended (the MK might be open as late as 11pm for regular hours) and you will have EMH opportunities.
Have a great time and maybe we will see you there!
cheers
jaysue