First, I'm going to explain about sentence ender ね (not interjectional ね).
It has several usages and among them, there's one that can be interpreted like English tag question. But there's a function that's shared by those usages. It is to indicate that information accompanied with な or ね is your impression or conclusion through observation (including recollection) in the moment.
For example, when you are talking to your friend on the phone, you can say 声きれいだね (which can be translated to "you have nice voice, right? / indeed / after all") . However, if you say 髪きれいだね, s/he will be surprised and respond as "Are you watching me!?".
That's to say, you can't use it like tag question unless you share the context with the listener.
On the other hand, 髪きれいだよね works even in that scene because よね can refer to what is not present in your observation.
In the situation where you can say 声きれいだね, if you nevertheless use よね and say 声きれいだよね, it feels a little uncertain compared with one without よ.
As for difference between …ですね and …なのですね, when they're used in confirming what the opponent have said as it is, they aren't really different.
When you confirm your interpretation of the opponent's remark, なのですね works, but ですね is only taken as your impression to the remark.
When you ask for agreement, …ですね works but なのですね doesn't make sense.
It's tough to cover up all the usages, but each です and なのです can be combined with each usage of ね. Difference between ね and よね will be parallel.