Wheaten crossed to any other true-breeding color will give mixes, no Wheatens. Blue Wheaten and Splash Wheaten can be interbred with Wheaten just fine, because the only difference is whether they have the blue gene or not.
You could cross the Wheaten hen to the Black Copper or Blue Copper...
No, you will not get wheaten marans from either of those crosses.
I think Black Copper and Blue Copper would be equally good for breeding.
If one is better than the other, it will be individual differences, not breed differences.
The Blue Copper will produce some chicks that show blue and some...