Ad blocking without rooting, OR low-risk rooting
Answering your first and main question: Ad blocking without rooting

On non-rooted devices running Android 4.1.2, 4.2.1 and higher, Adblock Plus will filter all WiFi traffic, but it needs to be configured as a proxy server manually. Detailed instructions are provided by Adblock Plus for not experienced users.

https://adblockplus.org/android-about

Avoid making multiple questions in one single post, make a single one for each single question.