I'll speak from my own experience. I support myself as a freelancer, and I have a child (he turns seven months next week :) This means I don't have much spare time to muck about with inane projects like writing a roguelike. But of course I do. I have no professional computer expertise, and really no experience programming at all. I played around making "Fighting Fantasy"-like text games in BASIC when I was a kid, and that's basically it. I chose to try to write a RL in Python as a hobby a long time ago. I can go months without looking at my code, and then have short sprees where the game gets some new features. A rule of thumb is to always leave the game in a playable state, and without too many loose ends in the code. If you can pick it up after half a year, skim some old todo-notes and say, "Ah, yes, I was just finished with X, and wanted to implement Y", it will make the whole thing much more enjoyable.
If I decide to take the work all for myself, can I learn a program language in my situation?
Yes.
How many hours will this take?
Pick up a good tutorial, and start skimming some of the stupid "hello world"-like exercises, to learn the basics of the language. When you know how to add and subtract, you're good to go ;) Remember to use official documentation, not just random tutorials on the web. You'll have a general overview after a very short time. After maybe an evening of studying, you can start toying around with text-based programs that take some console input from the "player" and prints a character sheet with randomized stat values in the end. Once you get the gist of it, you'll pick up what you need as you go along. You'll almost certainly scrap (big parts of) your infrastructure several times, but that seems to be true of everyone writing a RL.
And then, how much time could require a project let's say with an ADOMish depht but also graphics and stuff?
Many years.
#2- I fear that when I'll have learnt how to code, all my passion and game related creativity will disappear. Maybe it's a stupid irrational feeling, but who knows.
Who knows? In the worst case scenario, you'll gain a new skill, and hopefully you'll have had some fun in the process. As long as you remember to always take yourself with a grain of salt, I don't see the problem with picking up a hobby to see how long it interests you. It seems to me that paying someone to write the game for you is just folly. The whole fun is to do the development yourself, and you can't expect to keep "visionary control" of a project that other people are in practice realizing for you. Developing something as complex as a RL (and probably any useful or fun application) demands a lot of improvisation, swift "foot work" and clever tweaks to realize your ideas (which always turn out to be extremely vague once you sit down to code them).
Edit: That's not to say that all RLs must be one-person projects (as proven by several games). If you feel meek, but not too meek, you could focus on graphics, for instance, and you would naturally have impact on the whole development process based on your input. (If you deliver sprites for four new critters, and maybe throw some ideas out concerning which properties they might have, you'll soon download a snapshot of the code, where other contributors have fusioned your ideas with their own, resulting in four new, hopefully fun monsters).
As always,
Minotauros