Does having templates like this:

#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define pb push_back
#define eb emplace_back
#define F first
#define S second
#define sz(x) int((x).size())
#define rep(i, a, b) for (int i = a; i < (b); ++i)
#define per(i, a, b) for (int i = (b)-1; i >= (a); --i) 

useful in anyway or is it just preference?

Whats the best source for solutions in english after contests other than the official ones? I often find official ones too short and hard to understand especially for harder questions (div2 D and E+).

Any good book thats worth the time?

Is there any stat on whats the average rating of each question of div1 and div2? Like whats the average rating of a div1 B in that last 2 years?

Found these codes of someone from the recent div3. Looks like he has encoded his code in such a way that its doesnt get detected in the current plagiarism checker. div3F — https://mirror.codeforces.com/contest/2036/submission/289567963.
div3E — https://mirror.codeforces.com/contest/2036/submission/289541885. Mike please improve the plag detection system so that these kind of stuff gets caught.

What does it take to solve questions rated 2000 to 2500 that are not required for questions in the range 1700 to 2000.

What are the extra topics/skills needed to solve div2 E compared to div2 C/D.

Please provide an option to download the entire testcase like CSES. As of now testcases are just partially visible.

It would be really helpful if people who have more than 1 contest skipped get a "CHEATED" mark on their graph like CodeChef. Right now there isnt any consequences for cheating except that that your code gets skipped.