One thing to keep in mind is that they'll start admitting guests 30 minutes prior to the start of 'early entry', so if you want to be near the front of rope drop crowds you'll want to be there more than 30 minutes before early entry starts.
MK - From the DVC side I sometimes prefer to walk to the TTC and take the ferry from there, but overall this timing looks right. They'll let guests into MK at 8:00 and into early entry/rides starting at 8:30.
EPCOT - If you want to rope drop Remy's Ratatouille Adventure, keep in mind that you'll be coming through Future World and thus have a pretty big queue of International Gateway folks built up before you make it to the back of the park. On our last trip, we went to MK, took a bus to Beach Club, and walked from there to the International Gateway. We were into the park around 9:00, they let us through to the Remy queue at that time, and once the ride started loading at 9:30 we had a 20-minute wait. If we'd come in through Future World we would've had a much longer wait.
DHS/AK -- They'll let guests through the main gate no later than 8:00. At DHS, they let you into the central plaza where they break guests up into 'pre-queue' groups for Toy Story Land, Star Wars Land, Sunset Blvd, and Mickey & Minnie's Runaway Railway. If you want to be closer to the front of those queues, you may want to aim to arrive slightly before 8:00 regardless of your mode of transportation.