1. The DP special works but you have to change the 'origin' of the part you are trying to duplicate. This can easilt be done by selecting to move tool...you will see its centred on you object...hold down the 'D' key and then the 'v' key keeping both held down...you can now move the origin and it will try to snap to verts. Pick a vert on the face/edge/vert that you want to transfer the origin to. Now when you Dup special they will be together...but they are still seperate meshes. It depends whether or not you want them connected or not...this is another added part of merging the meshes. Merging will not alter the other part of the head when you model unless you have reflection turn on in the move tool. Or you can Dup special in 'instance' and it will mirror your movements I believe...
2. Depending on what version of Maya you have...hitting the 1, 2 , 3 keys will give you a smooth preview.
3. If you cant see your tools hit the '+,-' keys...they will increase/decrease in size, I dont know why they disappear though?? they shouldnt, Im not sure what you mean here?
4. Thats what it does...no you cant stop it. To get back to where you were just CTRL Z mate..it will take you back to the verts etc you had selected.
5. Im not sure about this one...if you want to delete a 'face' you have to be in face mode. If you want to delete and edge entirely with any unconnected verts on that line...'Edit mesh>Delete Edge/Vertex' this will delete all entities along that edge line.As far as I know Maya will not delete to anything smaller than a triangle, so you wont be able to delete that edge..it also doesnt delete border edges.
Hope this helped
P.S remember this isnt blender mate LOL I have same issues though mine are Survey software vs Maya..in a lot of cases you will run into this.
"A Darkness at Sethanon", a book I aspire to model some of the charcters and scenes