You have two separate questions, right?
Getting to your 5:50 is possible assuming all goes well--meaning your flight is on time, you don't wait too long for the bus, and you check in quickly. Then of course, you'll have to catch the boat at WL to get to MK. I think it's possible but really hard, and if I were in your position, I'd try to do CRT another night (cause you sure do not want to miss that one!).
About making ADRs: I know the feeling about being overwhelmed. I'd advise you to take a quick look at the touringplans.com website for the best and worst days in each park for the days of your trip. Then, have a rough idea of where you plan to spend each day, and plan your ADRs accordingly.
Here's what I did. On days we're in MK, I have my ADRs at convenient spots, like Chef Mickey's, 'Ohana, and Whispering Canyon. On a day we're in Epcot to tour, I have an ADR in Epcot. You want to minimize your travel from park to park to far flung resorts. Another example: we're staying at the Poly but we'll be doing dinner at Boma after our AK day. That's because AK is so far from the Poly, and I don't want to take the Disney bus all that distance on two separate days. I basically did the same thing on our last trip, too, and it worked well.
Have fun! And welcome to the boards--they'll drive you crazy, but you'll get lots of great info here!