Twice we've done three parks in one day. But I'm far from new to this. If you are new to WDW, and don't know your way around, it would not be worth it to try. You'll spend too much of your day doing nothing and feel like you wasted it. Since you didn't really read the hours of Epcot correctly, I'm guessing you're new to the parks. If you spend an entire week entirely at WDW, you still will not see everything.
Having said that, having long hours to work with really helps, as does acess to EMH. (What would a room at a value cost?) March is usually fairly crowded, but mid-week is better than the weekends. Avoid MK in the mid-day when it's most crowded.
Epcot doesn't close at 7 - only Future world - and Test Track stays open until park close. The fireworks happen at nine, after the rides stop (although if you are in line for something at nine, they will let you on that ride, but you'll miss the fireworks).
It can be done, but probably the last park you wouldn't get to go on much. The last time we did it, we had breakfast at MK, hit a few rides while lines were short. Then we went to AK , and went on most of the big rides there (the only show we saw was the bird show). Last, we went to MGM, and we were able to hit a few things there - before 8pm! But we knew what we were doing!
Another time we had from 9am until midnight - we did MGM - Epcot, and after the fireworks were over, MK was open until midnight, so we said, 'why not?" and raced over there. It was awesome! Even if we didn't go on much at MK - it is so much fun going in when everyone else is going out - makes you feel like the park is yours!
One trick of being offsite would be getting back to your car at the end of the night. (taxi?) Also, make sure you are at the gate at park opening - this can be difficult. It usually takes people longer to get there than they think it will.
Next, you kind of have to wait and see. Don't try to plan what you can't plan. Sometimes we're wiped out by nine pm, other times were able to cruise until midnight. You can't really plan for the crowds. Your best bet is to check the boards when you enter each park - go to the rides with the shortest lines (excpet the first park you hit in the am - hit your favorites there first). Aim for a few things - so you have an idea of where you want to go, but be flexible. if something has a short line - go for it. If you happen to walk by a show when it's starting - go in- otherwise don't wait for it. Dine QS. Don't sit down any more than you have to - there will be time to 'rest' while you are standing in line. Eat snacks while walking. Take bathroom breaks when you walk by restrooms - everyone goes when one person has to go. Don't wait in long lines for bathrooms - if the line is long - wait until you get to the next one. the same is true for food. Choose food options where the lines are short, esp eating at off times (have ice cream at noon, lunch at 2-3pm). Use Fastpass! Walk quickly from place to place (without being rude), don't dawdle like most people do. I wouldn't waste time on the surround movies, parades, or waiting in line for characters. Parade time means shorter ride lines! Popular meal times (noon, 6pm) mean shorter lines for rides!
Get in shape before you go - take at least a 45 minute walk each day - even if you are young - and walk as quickly as you can. There is a difference between walking and running. Don't run - walk.
It can be done, but two days is better by far!