I'd say the most important thing is to plan a mini-vacation and try to get a reservation for three days in the park (plus driving days). That way, you can pick the best weather day for Katahdin and use your other time there to explore the ponds and smaller peaks.
The next question is whether to be on the west or east side of the mountain. I've not stayed at Roaring Brook (drive-in, east side) or Chimney Pond (hike-to, east side) so I'll let others provide the details, but I believe they provide the short way up.
If you want to stay on the west side, I recommend Katahdin Stream campground, which is directly on the AT (Hunt Trail). Anyplace else, you'll need to get up wicked early and drive to your starting point, but here you can roll out of your tent or lean-to and onto the trail.
If you're looking to finish the 4000-footers (67 Northeast plus your ADK 46 plus Catskills = "The 115") then make sure to grab both Baxter and Hamlin peaks on Katahdin, and use a day to tag North Brother, whose open summit has gorgeous views *of* Katahdin.
Want to climb more? The Owl and Doublehead are both very worthy peaks. The Owl leaves from Katahdin Stream campground, so if you stay there, you're already lined up for it. Doublehead can be done from Kidney Pond, or better yet from the Kidney access road, since that trail will take you past a series of beautiful ponds. Want to canoe or kayak, there are some available for $1 rental, or bring your own.
Read up on how reservations work, and all the good stuff, at
http://www.baxterstateparkauthority.com/