You can turn sync off, open Gmail and press the three dots top right. Select settings and your Gmail account name, now tap where is says "Gmail sync is on". Now you can either turn all sync off from the pop up that appears by unticking the box in the pop up or select your Gmail account again from this pop up and untick all feature you don't want to sync.
I think if you have issues with Google tracking your usage then a device like this is not for you, Google can not only track what your usage but they can also track your location. To turn this off go to Settings, Location services and untick all the boxes there.
To some these features are prying but they are anonymous and for data analysis, they're there to see what's trending, what people are interested in, market research if you like.
If this concerns you would the knowledge that Google has a back door into your device bother you? If a application is deemed rogue or malware then Google can remove said app from your device without user input.....
I think some would find that shocking...