Hi,
As far as concern #1 goes, it should hang normally like his other ear, given enough time. He is still such a young pup and he has a lot of growing to do. I hope that you don't get his ears cropped; they are so cute with long floppy ears!
As far as concern #2 goes, I have seen a lot of Dane pups that look kinda skinny but they eventually fill out and become big beautiful animals. They grow very quickly and it seems that a lot of them just don't put on the muscle fast enough. A couple of things to think about however . . . Are you feeding him a premium quality diet? Has he been dewormed thoroughly? Is there any vomiting or diarrhea? Is he active and playful? You may want to feed him more frequently; 3 or 4 meals a day may be preferable if everything else seems to be fine.
Are you really feeding him 8 cups a day?? I hope that was a typo because that seems like a lot of food!
He will likely fill out after his neuter . . . but he will fill out anyway as he gets older.
Good luck. He's lucky to have such a caring owner.