Hi Pirate Papy,
Aires etiquette? Yes and no, I would recommend that you observe what others do around you and do likewise
No camping, in that you're not supposed to put chairs etc out but see what others are doing.
Park with consideration so that you don't take up more than your space - in this instance don't follow the examples of others if they spread themselves out...
Arrival time, during busy times then early afternoon generally works for us. You'll frequently find late arrivals looking for space at 10pm or so.
Carry disinfectant wipes for water taps just in case someones been using it for cassette cleaning.
I'm sure others will have more advice for you.
You could also check all the Aires listed on Club Motorhome as many of them contain real feedback, photos and videos which all help with your planning.
Happy travels