For about a pound and a half of ground beef, I mix together an egg, half a cup or so of bread crumbs or oatmeal, a good sized handful each of chopped bell pepper and onion, plenty of salt and pepper, and blend it all together before mixing into the meat. That way it only gets mixed once, and I definitely agree with others that overworking the meat results in a tough meat loaf.
I don't sauté the veggies first, and haven't had any problem with them being crunchy, since the meat loaf bakes for at least an hour.
I've used milk to soften the bread crumbs before, but haven't done that in a while.
I don't use a loaf pan - I form the mixture into a loaf about the size of a loaf pan, and bake it on a rack in a shallow casserole dish so the fat drains away.
I love meat loaf, and the main reason I make it is for the sandwiches.
Now I'm going to have to make one, it's been a while.