Welcome to the world of chickens!
If I recall correctly, Silkies are more likely to sleep on the ground or in the nest boxes than on roosts. Don't quote me on that
As
@Folly's place said, check the Silkie threads. That said, IN GENERAL, chickens will roost as high as they can get so you want the nest boxes LOWER than the roosts.
And 1 nest box will serve 3 or 4 hens so you don't really need 10 for your 14 (hopefully) girls. You will find that some girls will have a preferred box and get real pissy if another hen is using it AND that many hens will choose a box that already has one or more eggs in it which is why people put fake eggs in the boxes.
Of course if Silkies don't sleep on roosts, you are likely going to find them in the nest boxes that are near the floor. BTW, there should be a board across the front of the nest boxes a few inches higher than the depth of the nesting material to keep it from falling out or being pushed out as the hen settles in.
I agree, more ventilation. It is WAY more important than many people think. Chickens wear their down coats 24x7x365 so keeping warm isn't the problem some think it is. Just make sure there is no wind blowing over where the chickens sleep.
