I'm not sure that the margins are the problem. I moved them to their sides before putting the carriage back. As you can see on the video, the space bar and keys work fine, so the escapement must be engaging somewhat properly. The problem is that I can't use the carriage return. I don't know what else to do. 

I found a post on reddit of a guy that had the exact same problem https://www.reddit.com/r/typewriters/comments/64gjcj/hermes_3000_carriage_replacement/

He contacted Typewriter Justice on YouTube, and Charles gave him the following answer:

"(...) You CAN do it! It just takes a bit of wiggling, some jiggling, a little bit of luck and a gentle, steady hand... 1. make sure the mounting plates are lined up correctly, and check them often as you work 2. make sure the backspace pawl is away from the starwheel before you begin 3. move the carriage bottom plate all the way to the end so you can see what you're doing(or at least HALF of what you're doing) 4. insert it from above & a little bit behind the machine, along a diagonal plane...not just vertical 5. as you seat the carriage bottom plate, move the carriage a little bit to encourage the escapement to engage properly 6. BE GENTLE, TAKE DEEP BREATHS, AND IF YOU GET FRUSTRATED GO DO SOMETHING ELSE FOR A WHILE(seriously) (...)."

But I must confess that I don't exactly what I'm doing differently. It's not easy for me to follow instructions like this, I'm more like a imagetic kind of person haha.

I'll keep trying though, but it's getting really boring. I guess I understand now why people say that although Herms 3000 types amazingly, it's over-engeneered. They are not democratic at all, it seems that only experts can work on them...
 

The thing is: in my mind, I am doing what he's suggesting. But I'm probably wrong. Well, imagine a non-english speaker amateur trying to get written instructions in english on how to replace the carriage on a Hermes 3000... hahaha. 1) About the "mouting plates" - if he is reffering either to the plates of the carriage on both of its extremes, where the screws go, or the plates of the machine that receive the carriage, I'm sure I'm trying to keep'em as lined up as possible. 2) about the "backspace pawl": I pressed it a few times to see how it works and tried to keep it away from the starwheel; 3) I keep moving the carriage to both sides so I can see what I'm doing on each side of the procedure; 4) Now, here is one of my doubts: what does he mean by diagonal plane? Cuz one thing is to lean the carriage sidewise on a diagonal plane, to insert first the right side of the carriage and then the left side, and another thing is to lean it backwards or foward to insert both sides simutaneously on a diagonal plane. Does this make any sense?

By 'mounting plates' he means 'turnbuckles'  Same thing, just different words to describe.  By 'diagonal plane'. I think he means to tilt the carriage backwards a little when holding the ends in your hands.  Don't just lower it straight down.   You shouldn't have any need to either operate the backspace or spacebar when fitting the carriage.  I can tell that you are getting frustrated with this.  Just take a break, maybe even a couple of days, and then go back to the problem.  I repair typewriters professionally and sometimes I need to take a break away from a machine and go back later.

Ok, I finnaly made some progress. I reinstalled the carriage and it's working. But it's not working 100% correctly. As you can see on this video (https://youtu.be/OCQpimdQY3Q), the carriage is now making a clicking sound, completly opposite to the smooth soundless movement of Hermes 3000's carriage. Any tips on how to proceed from now? I tried different positions for the screws that hold the carriage, but without success. 

Here are some photos of how the carriage is screwed.