Yay! Congrats for trying out the Raw-side! Let's see if I can answer some of your questions... First of all, to find out the amount you should be feeding daily, multiply to find 2%-3% of his estimated adult weight. Assuming your guy will grow to be average sized, you can figure he'll be around 65 pounds, you should be feeding between 21 and 31 ounces per day. So you're doing great feeding 1 1/2 pounds per day, and may need to feed another 1/2 pound or so. Use your dog as a guide of how much to fed him. If he looks a little thin, you can feel and clearly see more then 2 or 3 ribs, up his food intake a bit. If the ribs disappear, feed less. Puppies sometimes need the higher amount recommended. Since he's only 8 months old, you should break the amount up into 2-3 feedings per day.
It's usually easiest to start on one single protein source with a little more bone then you would normally feed to help firm up the stools to begin with. Chicken leg quarters or bone-in chicken breast would be great. You should probably remove the skin/fat for the first few days at least so as not to overwhelm his tummy which could result in cannon-butt! :eek:
I would hold off on adding organ or other protein sources for at least two weeks, and then only add a tiny fingernail sized piece at first.
As far as supplements go, you do not need to give any! (And fiber is a grain=undigestable) It's like throwing the fiber away so I wouldn't waste money on it

The dog will get all the vitamins/nutrients he needs from eating meat, bones, and organ. Some people who do not feed fish in the regular diet do choose to give salmon oil capsules, but you could just feed a fish once a week or so...
As far as the juice thing, a dog cannot process fruits or veggies so it would have absolutely no nutritional value to him at all, and could cause digestive upset, so I would skip it and just stick to the diet.
Hope this helps some! Please don't hesitate to ask if you have any more questions
