So, I feel kind of overwhelmed with all the different ending in the game.

Supposedly the game has 3 different main 'routes', one play trough is around 18-19 hour with all paths taking around 50-55h total .

Is it worth to complete all of them ? do the endings have different enough story to justify it ?

When do I make a choice to go to different A, B or C endings ? is there some non-spoiler guide that would help me out to not play this same route 3 times, or go totally unnecessary path ?

You've been caught up in a bit of the poor nomenclature this game suffers. There aren't really any 'routes' with distinct endings. You start at A which will lead directly into B which leads into C and so on. The main story consists of these A through E 'endings'.

There's really only one decision point that will affect any of this and you won't need a guide to spot it.

So the best advice is...just dive in and have a good time.

Think of Ending A as the ending to Chapter A, Ending B being that of Chapter B, and so on.

The "endings" are chapters. No Telltale or Quantic Dream style of split paths or decisions to be made. Just go through the game doing as much or as little of the side quests as you want to. But remember that you're not done until you see ending E.

There are technically 26 different endings, but all endings after E are generally one-off bits that dump you right back into the game after a very quick credit roll. As has been mentioned, A goes directly into B and into C or D. Once you have completed both C and D, you will go directly into E. It is necessary to complete the A through E endings to see the entire story, but it is not like playing the same game multiple times, as it is new content each time through.

Exactly as has been stated, just play through the game. There's nothing special you need to do to get the "endings" that matter.

The confusing terminology of the game has been covered by prior posts, but I'd also like to point out that 50 hours is a massive overestimation. Steam has me at 33 hours, which was the entirety of the story (A-E) and a decent chunk of side content (though not all of it). It's certainly possible to put 50 hours into the game, but anyone telling you it's a "50 hour game" is exaggerating. I saw all of the story and a lot of the side content in my 33 hours, and if you wanted to do only the story you could do it in a lot less.

As other have said, just play. Most of the endings are funny little asides that really don’t matter.

If you just keep playing, you can’t miss the endings that matter.

The game will lead you through all of the main endings. It'll run you about 25 hours if you don't get caught up grinding (which you won't need to do, since the game is very easy).