Great project! As far as your Barne X Cream Legbar crossing goes. You should get a darker egg if you use a Barney rooster over Cream Legbar hens, but either combination can be used.
Punnett's research in egg color genetics showed that there is one gene for the blue egg color, and more than a dozen genes for brown egg color. Some of the brown egg color genes are sex linked genes so the rooster contributes more brown genes than the hen to the pullets of the cross.
As far as the auto-sexing goes, a Barne Roo (who is not barred) over Cream Legbar hens (single barring gene) will produce a sex link. All the pullet will be non-barred and all the cockerels will be barred. This would similar to your Barne X Barred Plymouth Rock.
If you reverse the Cream Legbars (roos with two barring genes) with the Barnes (non-barred), then the sex-link is lost because both the cockerels and pullets will receive a single barring gene from the father.
For your Barnebar, you will need to produce a roosters with two barring genes. You currently have single barred rosters breed back to Barne hens. You can breed the Barred Barne hens from that crossing back to the Single Barred roosters and you should get 50% single barred 50% double barred Barnebar roosters. Breeding the double barred rooster to barred females will produce auto-sexing offspring with all the males being double barred and the females only single barred.
