I just ordered the JDM DD kit from Riverside but I did not ask about the antenna and wire harness adapters...will I need them for an aftermarket head unit?

I tried to search the topic but nothing was definitive.

 

metra/bestkits 7550
antenna adapter is the standard nissan.
There should be MANY definitive threads as I've answered the question MANY times. The 7551 is more likely to relay engine noise and unless you have a high preout deck the overall volume will be MUCH lower.