I have 4 versions (http/https) x (www/non www) of my website in search console. But I realised that I needed search analytics information on a subpage's ranking on google, but when I check search analytics, I didn't have this information for my subpage.So I have added this subpage (https://www.example.com/mypage) as a new site.Q1: Is there any negative affects of this action ?  Q2: Is that a rational action ? I mean, am I on the right track for my goal?Q3: Is there anything I should do more? (Like adding 4 versions of this subpage, or adding a sitemap, or any other thing that I can't think of.)
Adding Subpage to Google Search Console (Things to be careful)
seo;google analytics;google search console;google search;search results
To check final page ranking (like www.example.com/this-is-my-final-page-and-there-is-no-any-subdirectory-after-that/) you can use search analytics reports without adding new property into search console. To do that click on pages option and add your final URL like this.If you want analytics reports at section level like www.example.com/sub-directory/ then you can create a new property into search console and add canonical version of website, for example if you open www.example.com/sub-directory/ in browser and it's redirect to https://www.example.com/sub-directory/ then add only https version properly, there is no need to add all variants in most cases (Check oskar Skog comment). Now let's comes to your questions.If you've parent property www.example.com as well sub directory www.example.com/section/ then you'll not going to get reports on both properly, here parent property will win here according to this doc. So add sub section properly only if you've very big site and want search analytics report at specific section.I will add multiple section property into search console only, if my website is very large and I have really big section on my site, like www.example.com/tutorial/ and www.example.com/news/ etc. otherwise to track final URL, just check my first screenshot.You only require canonical version property, other variants(at section level) will be empty and will not going to show any reports.  Remember: Google will show search analytics report only for indexed pages, and Google index only your canonical version of URL, not all variants with http/https,www/non-www.