Therefore, the forum is mainly used for bug reports, and improvement requests, instead of flyspray (which is anonymous, beside a simple email address, and not linked to main user profile).

Not important at all, it could just save some time for developers and reporters, and let the forum being more an "user to user" communication channel rather than a bug report system, as it is today.

Note: I will try to build the software tomorrow or the day after (with eclipse), I will let you know how it goes : I am more used to "raw" systems (like the Linux kernel or Apache, where I just need git and my favorite editor) than to integrated software tools

Indeed, the forum is rather intended for the users whereas Flyspray is used to register and follow the work of maintenance and evolution.

I personally use NetBeans as a development interface, while Jean, my developer companion, uses Eclipse. But you should be able to do without one or the other and use your usual tools. It should be noted that originally StoryBook was developed with Eclipse.