thanks everyone !
@ErichWK I'll try too post some timelaspe to show my process (both for tileable texture & rocks alone) and for my diffuse too.
I use mostly trim dynamic & trim smooth border (customized a bit) with some alphas, some clay brushes (with alpha again)
I also use a custom insert mesh brush to add some small pebble (but again, i'll make a video tutorial later)
@Cordell Felix thanks, this one got a specific set of diffuse & normal (i'll post them tomorrow) but I'm almost done with the first tileable texture
@dissonance Thanks for the link ! That's a nice idea to add those details, with these rocks I'm trying to stay generic without too many flashy details, since they will be used to populate levels, and there will be many of the same model duplicated everywhere ^^, but again, thank for the link, I'll check it out!