Hello Sanne,
welcome on board :-)
I'm Dutch too, grow several sorts of orchids: Phalaenopsis, Oncidium alliance, Australien Dendrobiums like kingianum and xdelicatum, Den. nobile and Ludisia and Pahphiopedilum.
A great way to determine when to water orchids is using a skewer, for instance a "satéstokje". Stick one in the middle of your pot and leave it there. Use always the same hole to stick it back. When you are about to water the plant, pull it out, and look/feel the stick.
For Phals I want them to look dry but feel a bit cold when I hold it against my lip.
After a while you can feel on the weight of the pot if they need to be watered. By the way, if the roots look silverish, but you can see tiny water droplets on the inside if the pot (when they are in translucent pots), don't water yet ;-)
You bought beautiful Phal's and the pictures are beautiful! Be careful, once you got bitten by the orchid bug...
your collection will grow!