At Amsterdam airport, even though we speak about terminal 1,2,3, everything is under one roof. No separate terminal buildings. So, to answer question 1, it is not complicated at all: you simply make your way from your arrival gate to your departure gate. Arriving from the USA and staying airside: no passport control or security to pass. So questions 2,3 and 4 don't need to be asked, not applicable to you. Finally: yes, there is the KLM non-schengen lounge, but Premium Comfort doesn't give access. But paying for entrance will if it is not full.
Now, i am local at AMS, so not used to transfers coming from NY and going to Jo'burg. So, fellow FT-ers, correct me if i am wrong here.
I wish you a very relaxed transfer at Schiphol