As for editing the three movies together, it's actually quite simple. The transition from I to II is easy as hell, since the ending of the first film repeats at the beginning of the second one (right before Marty opens the garage and Jennifer enters the scene... this way the switch between Claudia Wells and Elisabeth Shue isn't that distracting). Cutting out the credits in II works too... I cut from Biff's line about "A flying DeLorean...?" right to the the trio re-entering Hill Valley 2015 (with a little sound editing to remove the beginning and end of the main theme). As II and III were shot back to back, editing them together works like a charm, and with a little AfterEffects knowledge painting out the titles from III can be done.
Yet I would advise doing this as an XviD or DivX edit on DL-DVD... most players play these files, and you won't have a noticable loss in image quality.