Do yourself a favor and get your hands on a copy of the Unofficial Guide. They have generic Magic Kingdom touring plans to fit several "typical" categories of people (i.e. with young kids, without kids, 1 day, 2 day, etc.). If you need a more customized touring plan, you can go to
www.touringplans.com (brought to you by the same folks that put together the Unofficial Guide) and have one generated (for a fee) that meets criteria you specify.
According to the DIS, it typically takes 20-40 minutes to get from POR to MK using Disney transportation. Generally speaking, this would mean that if everything goes right (the bus is there when you walk out of the building, takes off right away, and hits mostly green lights) it will take you 20 minutes and if everything goes wrong it will take you 40 minutes. Of course, during the busier times it could take even longer. Based on this, you probably want to leave POR an hour to an hour and a half before the EE time so that you can get there, get through the gates, spend some time with the characters and then make your way up Main Street for the rope drop. It really depends on how much time you want to spend with the characters - there are normally a pretty decent number of them scattered around the entrance to Main Street, but each one of them usually has a queue (based on popularity). The downside to doing the characters before the rope drop is that you have to get there even earlier. The upside is that the queues for characters only will get longer as the morning progresses (particularly right after the "official" opening time) and this way you won't have to backtrack down Main Street.
Like tink2, we usually head to Fantasyland b/c we have two young kids. Dumbo, Winnie the Pooh & Peter Pan generally build lines in Fantasyland the quickest, but Winnie and Pan have Fastpass, so we try to get Dumbo out of the way first thing.
Have a great time!