It’s a bit outdated but most of the info you’re looking for is in the documentation and the links in my signature.
The reason nobody has responded to you is because you’ve asked questions that require really detailed answers, and people probably dont have the time to write it all out. Try to learn how the logic bricks work and come here to ask specific questions when you get stuck.
2.there is a new dynamic parent actuator. search for a user named OTO, he made a demo recently.
EDIT here it is: http://blenderartists.org/forum/showthread.php?t=125207
You should still look up OTO’s post’s , he had made a few really cool demos and tutorials, iwsh I had his website address to give you.
3.Look up the scene actuator (actually just look at it, it is pretty self explanitory)
4.You can just move the center of a plane, to the far left edge, scale it to your desired width, and snap an IPO key. move forward 100 frames, and scale it on the X axis to nothing, and snap another key. Use the IPO actuator, with the property setting, and make a property to control the scale of the bar.
Look up Triggers, it is basically either a ray or a collision sensor that looks for the player, once the player triggers it, send a message to the door to set off the door animation. (Message actuators need you to type a capital OB in front of all object names for some stupid #&$^ing reason)