Antonio,

I don't think one of your questions was ever really answered. You asked why the shoes you showed in your original post had both the three holes for road cleats, plus what you referred to as two "lines" between the three holes. The answer is that the three holes in a triangle is the standard cleat-mounting holes for most road pedals, compatible with Shimano SPD-SL series pedals, Look pedals, and others. But the two "lines" are actually two slots, each of which has a screw mount inside. These provide an alternate mounting for SPD type pedals, whose cleats only have two mounting screws. The reason for the slots is to provide some fore-and-aft adjustment (With the three-screw road cleats, the adjustment is actually in the cleat itself, not in the screw holes in the shoe.)

The two-hole SPD-type pedals are more usually associated with mountain bikes, but some road cyclists still use them - those Diadora shoes you pointed out take either pedal type. Mountain bike shoes will usually just have the SPD type two-screw mounting holes, and a lot of road shoes only have the three-screw mounting holes. Those Diadoras are just more "universal", in being able to use either type of pedal.

But for road use, the advice given above to get some pedals that use the three-hole cleat is good advice. (The main reason to use SPD type pedals is if you actually wanted to buy mountain bike shoes - which tend to be a bit easier to walk around in, since the cleat is sort of recessed into the sole. But since you are getting regular road shoes, it makes sense to get 3-hole pedals.)