Welcome.
This site has a very helpful planning tool called a Points Calculator. You can put in your dates, choose your location including the nonDVC resorts and it will tell you how many points are needed. Here is the link:
http://www.wdwinfo.com/resort/dvcpoint.cfm
As to whether it is good choice to use your points to stay at nonDVC resorts such as the Polynesian that is certainly a personal choice as to what the value is worth to you.
Certainly you can get larger accommidations such as a 2 bedroom villa at a
DVC resort for fewer points than a standard room at some resorts such as the Grand Floridian, but it might be worth those extra points to you. Just as it would be worth it to you, to use them to book a stay in New York City in a small hotel room.
As to making reservations. If you are a DVC member you book everything through Member Services. They can book your stays at any DVC resort including Vero Beach and Hilton Head and they can also book your stay at any Disney resort such as the Polynesian. There are times that the Disney resorts might not be available to book using points.
If you have any other questions please ask, this is a very knowledgeable group around here.