Every site using Google Adsense must have Privacy Policy. Privacy Policy shows seriousness of online business or concerns about the visitors.
In my opinion, every site should have a privacy policy. It shows you're serious and helps build trust with site visitors. It's not always necessary, but definitely something you should think about. Here's a website you might find useful: http://www.freeprivacypolicy.com/. Take Care, Alan
You can copy... no reason to try to write your own from scratch. Just make sure it's relevant to your site and change it as needed. The link I posted should have some good templates to copy from.
I think it is a must to have it own privacy policy. It can trust for the customers or clients. You can also check what others are saying and adapt it to yours. Usually, it does have to be complicated.
for adsense you just have to cover some basic things like cookies, you can find exactly what you need to include on the adsense help pages.