Hi Ailla, and welcome from me too. What lucky chickens you have. All that space is wonderful, but have you you thought about securing the perimeter of the run against predators? You don't say which part of France you live in, but another ex-pat member in he Dordogne has had a lot of trouble, not only with foxes but hunting dogs. It would be sad to lose your lovely new birds, so do read the threads about foxes etc and maybe get some electric netting. You could then enclose smaller areas and rotate the grass a bit.
It certainly sounds as if you have young POL pullets, and you should expect them to take up to another 4 weeks or so (maybe less) before laying if their combs are still small and pink. This is good, as they will have a week or two to settle in and finish growing, moving home is always stressful for chickens and older ones who have started to lay often go off lay for a while when getting used to a new place. When their combs get redder and they start inspecting the nestboxes without laying, then they are nearly there. It's good to leave the coop open all day so they can do this. Poo sounds fine, it should usually be fairly solid and the white streak is the urates, I.e, the urine part of the droppings, birds do it all in one go. They also do a more runny, smelly sort sometimes, called a caecal poo, which is also normal if it's sort of a one- off every few days.
Straw isn't very good in nestboxes as its not absorbent and is hard to keep it clean if it gets pooey, and also the hollow stems may possibly harbour redmite. Aubiose (shredded hemp stems, used as horse bedding and made in France) is softer, very absorbent and can be used on the floor as well as in the nestboxes. There are other types of bedding which you can use as well. It's good that they don't sleep in the nestboxes as if they can be taught to perch, they won't poo where they're going to lay eggs next day. Do they have a perch in the coop area? It needs to be 2 ins wide with the edges rounded off a bit.
You're quite right to clean up every day - if you can get some absorbent stuff on the floor, such as Aubiose, it's only a couple of minutes job to pick it up into a bucket and it's fab on the compost heap. Leaving it longer attracts flies and it will get smelly. If they don't sleep and poo in the nestboxes, just change the bedding when it looks as if it needs it.
Had you noticed the link at the bottom of each forum page to the main Poultrykeeper website? Lots more articles on there about all aspects of chicken keeping, very interesting reading.
(I'm going to move this thread to General Chickens, where it will be more at home. Any replies, please post under General Chickens.)