My golden retriever mix always pace around outside and bark at passers-by or visitors.basically she barks at almost everything (this is quite an issue). Other than that, she would sometimes sit around just relaxing,looking around but very alert. I hardly see her sleep for more than a few minutes. Even at night, I can hear her bark at the security guard patroling the neighbourhood. Is it healthy for her to be up most of the time and just have dog naps here and there?

He sounds still young. Dogs sleep with one ear listening until they are quite old. I don't know why you leave him out at night? Of course he feels vigilant; that's what dogs do. He's protecting you, for one thing. Bring him in at night.
If he's pacing, I suspect you aren't taking him for walks and for play in parks with other dogs or just a Frisbee or ball in the back yard. He needs tons of exercise.
Barking is a training problem. I am the last one to tell you how to train a dog to stop barking, because although good at other aspects of training, I've never taught either of my dogs to stop. They know NO of course, and try to muffle their barks, but they don't stop on command. It may require a muzzle.

Our dog don't live with us inside the house. She stays outside but we live in Malaysia where all the houses have walls and gates and fences around the yard. My dog has a doggie crib and a dog house but she prefers the grass or the driveway. In fact, she's always sleeping right in front our door or at the patio where she eats and drinks (also where her crib is). She is about a little over a year old. She does understand NO but it only stops her at that moment, and starts again afterwards. I don't feel like resticting my dog with a muzzle. Id feel bad for her.

Some barking is 'announcing' arrival of someone. You can tell the difference. When she barks, go out and say one sharp NO and then pat her. I have a feeling that in your area people don't spend much time with their dogs, playing or going anywhere, or training. Training is a TON of work. So you are going to have to put up with this. Hope the neighbors don't get mad.