fairymuff, bradtx, and djb, thank you very much for all your opinions, suggestions and advices; you went straight to the points I presented and that was most helpful of you.

In fact, on Saturday morning, I went for a test ride. Coming from a mountain bike, I noticed a considerable difference in the comfort, the starting power, the speed, the turning ability, ....

This bike is very light (again, my standard is a mountain bike), flexible, sturdy and comfortable (although the mtx bike is undoubtedly more comfy due to the front suspension). Changing rear gears is almost an imperceptible task.

Yes, the gears seem a bit heavy (later I found out that the front disk was not perfectly aligned and was somewhat responsible for holding me back).

In the end, I became very interested in this deal and lost my mind, freed my wallet and made the investment (so I try to convince myself). djb, you're absolutely right: if (I hope not) I end up not being satisfied, this model can easily be sold, contrary to what would happen with a "pure" touring bicycle.

I only added a cyclocomputer, some dual pedals, water cage and ordered a bike kickstand from BBB.

The next step (appart from getting more attached to this new treasure of a bike) is going to be choosing a rear rack, rear panniers, and mudguards. Could you give me some suggestions on brands/ models?

Considering mudgards, I've been told of this model (but the reviews are not very enthusiastic...):
Amazon.com : Topeak Defender Rc1 and Rc11 Mudguard-One Set (Black, 23.6x2.3x3.5-Inch) : Bike Fenders : Sports & Outdoors

About panniers, the brands: ortlieb, kordo, Agu

About racks: tubus, blackburn, topeak (blackburn seems to be a bit too expensive fot what they offer but I am totally new in the field).