I could not have planned this better if I tried. Decided not to make a trip to Den Bosch after all for some foamballs, as the shipping costs are lower then the price of a train ticket (and I would spend a day there, buying food and drinks and God knows what), so ordered some polystyrene balls online.
I'll do the two 20 and 25cm halves as gas giants, not sure yet about the 15 cm ones, maybe a cracked plates / lava world and a ice planet. Nothing overly fancy. The 2 each of 4 and 5cm balls will be moons, most likely with 1 or 2 full of craters like the other one..... Not sure yet if I will cut these in half too or just lop off a bit so they stand up on the table and glue a round base to them. Would have to check if I still have 40mm and 50mm round bases. Or just call Evin to cut me some.
Also nice, Urbanmatz sent me a message today telling me my mats have been shipped. Delivery in 2-10 working days. It is by GLS though, so I hope I'm home when they drop them off cause their depot is in Den Bosch.