Just my personal opinions of these brands.. I would not bother with Blue Buffalo. So many people seem to have digestive issues on that brand. I also do not like the company as a whole, seems shady. Orijen and Acana are imo very overpriced for what they are. So much beans/lentils/peas which in my experience are not very easy to digest. My dogs get gas and huge loose stools on foods that use beans/lentils as the starch source. I have had much better digestion results with foods that use rice/barely/potato/sweet potato, that is just my personal experience though. With all the odd cases of DCM/low taurine with dogs on Acana, I would hold off on that food anyway until more is found on that.
I am not too familiar with Innova or Solid Gold. Wellness seems pretty decent. My go to puppy formulas are Farmina Puppy and Annamaet Original Puppy or Ultra. It really is trial and error though, what works for mine may not work for yours. You will only know what works for him by experience.
As for mixing add ins, my dogs starting since they were pups get raw meat, boiled eggs, and tinned sardines added to their dry food. They are very used to this though as like I said this started very early on. I would not add in a bunch of stuff too quickly with your pup though. You could start with just some egg or chicken added in a few times a week and go from there.
