Hey! I hope this isn't breaking the rules (self promotion) but I wrote a blog post on how to change your new tab page: https://blog.nahtnam.com/p/my-new-favorite-browser

It is described under the "new tab page" section. I can't really comment on the privacy/advertising concerns but I do know that Opera providers a VPN for you (who know what they are doing behind the scenes) and have their own adblocker built in.