[ART] Many questions

[WALP]

1) select your object(Right mouse button) hit "Tab" to go into edit mode on the active object(the object you last selected). use the buttons in the header below to choose component types(vertex/edge/face) or hold CTRL + TAB as a shortcut. Select the components you want to delete and hit "Delete" or "X" to make a little menu with options for deleting appear.

Btw its these buttons I am talking About
2)Yes or im screwed ;D
3)Open up something that swings open/close from original amnesia in the model editor, and use it as reference.
4)You dont have to create seperate entities but you seperate them as different objects in blender before you export them. else you wont be able to edit the closet doors individually in the model editor.
5)You assign them to the same body in the model editor