When is it time to take a coach? I mean, if you try as much as possible to be autodidactic...

I am lazy in chess. I do a lot of stuff, like training endgames, openings and tactics, but I usually do not spend much time analysing my games. This is AFAIK one of the most important things to do to improve in chess. Perhaps I am wrong, but I think that I would learn a lot trying to analyse my games or to analyse the blunders I am doing in tactic training. I would probably understand where I show the main deficits in chess. Is there any good reason to take a coach to show me exactly the same things that I would (with the help of an engine) be able to sort out myself? The coach would probably take over the job that I should do. Or do I see the things from a wrong perspective?

I agree that hard work is the number one key element.  The way you explain what you actually do, does'nt sound like you're lazy...  If you ca afford a coach and you can find one that is compatible to your personality, it would definetely be a major asset to improve your game!  The social interactions with another person/a coach can be very beneficial to reassure you, inspire confidence, break bad habits and point you in the right direction.  It also depends how far you wish to go, how much time and money you wish to invest in chess... Are you quite content with playing games and competing in tournaments or do you strive for excellence?

Okay, this with "I am lazy" is not quite correct. Or let's put like this: I have an idea the amount of energy you have to invest to improve considerably in chess. So, I am certainly lazy when compared with somebody who is ready to invest so much. 

I would like to take a coach, but I am just thinking that for what I am doing now (I do not play tournaments, and my strongest opponents are here in chess.com) a coach seems to be a little bit exaggerated. It is as hugofianchetto said: do I want to improve in chess and invest energy in doing so? I think I will only be able to make a decision after beginning to play in a club...

Analyze your losses and master games. For something different, analyze amateur games around your level and find the problems

Joining a club and playing OTB tournaments will bring a huge improvement by itself, after you hit a plateau it could be the moment to hire a coach I suppose.

If you really enjoy this beautiful sport, I strongly recommend playing in tournaments: they are exciting and will be a mesure of your level of expertise.  You will learn to win and loose, you will realize where you're at and the amount of study you will need to improve.  If you play at your level in a suitable category you will feel success and it will motivate you.  If you play in a very strong category, you will have to be strong-willed to accept your losses and carry on.  Ultimately, play against stronger players will help you improve.  Here are the components of a chess education: playing games, having fun, studying your games and GM games, competing in tournaments, studying openings, tactics and endgames, getting in excellent physical shape (competing in tournaments takes a lot of stamina and endurance) and taking formal lessons from a coach that suits you.  I think that if you incorporate these components you will fare well.  And what is more: all your investments in chess will benefit you in others domains: personal psycho-social development (self-esteem and confidence, problem-solving skills...), career, etc. So, while you will work at becominmg a better player, you may also become a bette person... It's win-win any way you look at it!

Trying to learn by yourself is possible but almost by definition the slowest way to go.  The problem is that you don't know what you don't know.  We often think tactics are what holds us back, and that's definitely true, but why do those tactics happen?  We know that tactics flow from a superior position, so what are you doing wrong before the tactics start flying?

There are many common mistakes people make: premature attacks, defending when not necessary, defending instead of counter-attacking, trying to force a kingside attack when the Queenside is more accessible, not exchanging Bishops in hopelessly blocked positions, etc.  

These aren’t tactical mistakes, they are thinking mistakes, where you literally do not think the right way in the given position.  This type of mistake is extremely tough to fix on your own because you don’t even think of a different plan.  If you only think attack, then all the Queenside weaknesses in the world won’t help you.

A good coach will literally open your eyes.  This will then speed up your self-teaching, as you’ve gained insight into your typical mistakes.  It’s fully possible (and perhaps preferable given your stated ‘laziness’) to have 1 or 2 coaching sessions, then several months of self-study and then go back for a session to see if you improve in the given area.

Finding a good coach can be tricky, but an investment in education almost always pays for itself.  Good luck.