Ad blocking without rooting, OR low-risk rooting I have previously nervously rooted phones I've owned (Samsung S2, S3) as I wanted to be able to use AdAway ad-blocker, effective not just in browsers (e.g. AdBlocker) but also in other apps. I say nervously because I always found the mode in which these modified ROMs are offered (websites such as XDA developers) a bit dodgy/flimsy. Nevertheless, this has worked well in the past, but I am aware that I might just have been lucky, as those forums abound with bad experiences, i.e. bricked phones, or at the very least tons of wasted time trying to at least make your phone work again even in its stock let alone rooted firmware. 

Now I have a new phone, the most expensive I've owned so far (S7 Edge), and browsing these same websites again, I feel just as edgy performing this risky operation. For instance, the S7 Edge section of the XDA-devs website has several rooted ROMs available, however without spending hours and hours it is not obvious what the differences between them are. To name, just a few doubts:

1) how are 'recovery' firmwares different from ones just called 'Kernel' or 'ROM'?

2) in what way does each of those ROMs differ from the CyanogenMod, which I've happily used in the past but for which there is no S7 Edge version released from what I can see? Incidentally, I used Odin to install CyanogenMod on my old phones, rather than a 'recovery'.

3) are there major differences in how the S7 Edge will operate with such a rooted firmware/ROM as compared to the stock one? Specifically, will it be any more vulnerable to exploits etc, given that no-one can really tell whether these ROMs have e.g. built-in trojans?

Given all these concerns about Android rooting, is there any way that adblocking can be performed without rooting? If not, what is the least-intrusive and least-risky way to root an Android (in this case an S7 Edge)?
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.