You could leave him on the kibble for a couple of weeks and let him settle into your household, and then do the following ...swap out 1 of his kibble meals a day for raw. Do this for a week, then 2 meals for a week, then 3.. you get the drift
If was me I'd just start the swap straight away, but only use 1 type of meat (i.e. stick with chicken or turkey, don't mix and match). Also,
Just for your info the NI puppy food has no different composition than the adult food, the difference is the grind is finer on the puppy food; this may be important for you with a young pup, but when I used NI and we got Hazel she was 5 months old so we stuck her straight onto the adult mixes.
The mixing kibble and raw thing; It's not so much don't do it during the same day, the advice is around mixing in the same meal, however I mixed them in the same meal for a week, didn't do my girls any harm at all.
As an aside NI got me into raw feeding too - I really liked it, but be careful as not all of their foods contain offal meat and sometimes my girls got constipated on it. I use RawToGo now who are a Durham Animal Feeds distributor - not as prettily packaged as NI but lots of varieties and the girls seem to like it and aren't constipated any more