Are the curtains custom as well or can they be purchased?

Yes... the curtains are custom. Sorry!

What size is the rug?

The rug is 8 x 10.

I looked at the Au Lit website and couldn't find the bedding. Do you remember which it is?

This is the fabric for the duvet cover. The colour is Cream: http://www.aulitfinelinens.com/collections/cotton-satin-duvet-covers/products/boheme

Au Lit can custom make their bedding so you can use a combination of fabrics for the flanges and headers on the sheets and pillow shams. You will not find the exact combination on their web site because this was a custom order. The Euro shams in this room are not from a bedding store. I designed them and fabricated by our sewing workroom.

what color is the ceiling? such a beautiful bedroom

The ceiling is Benjamin Moore's HC-173, Edgecomb Grey at 50% strength.

When you dilute a paint color to 50%, is there a specific shade of white recommended?

No... When they mix the paint they use half the pigment in the usual amount of base.