6 weeks is very young to be removed from litter, however at 6 weeks he can eat kibble and I would most definitely start him now.
Young puppies should be feed about 4 times a day. There are lots of good quality dry kibble to choose from and definitely start him on the puppy version, he could move to adult within a few months.
If you decide to go with Royal Canin, the Maxi Junior is suitable for large breed puppies, I would start with about 3 cups spread out over 4 feeds, increasing to 4 cups by 3 months.
I used to soak the kibble in water for a about 20 minutes as this helps with digestion and then add a little bit of extras such as goats milk, or dollop of plain yoghurt, or tablespoon or 2 of ground mince or cut up chicken etc.
I haven't used the Royal Canin puppy milk, however goats milk is pretty good.