Raingirl, its good to know that you're doing research before you get a dog. Grab some dog care books and flip through a few...its definately a good idea to be FULLY prepared before you think about getting a dog of any size.
I feed mine 2 times a day. She eats Wellness, which I consider a good brand. Three is too much in my opinion, unless of course the dog is a puppy. I also don't feed my dog DOG food all the time. She does get people food..cooked veggies and meat, pasta, rice, etc...a dog gets bored eating the same thing for its whole life..lol I definately wouldn't recommend it.
The amount you give a dog definately depends on the size and the current weight condition of the dog..mine gets 2 cups a day..and she's 57 lbs. It all depends on what kind of dog you get..remember, dogs need alot of exercise to keep them in shape too...and never get a low quality dog food..it'll cost you in the long run...
Good luck..I hope you do some good research