Making new breeds is a long project. You are worried about small eggs, weird egg shapes, etc. in the legbars and you are sure to see all that an more if you are creating a new breed. Since you already have a hen flocks of one breed and a sire of another breed you could just breed hybirds. The Wheaten Marans hens crossed with the Cream Legbar sir will produce the green eggs that you desire. The hens will NOT be bars from that crossing, but the males will get one barring gene. The chicks will have the chipmonk pattern so you will probably be able to sex the cockerels and pullets at one day old from the sex-linked barring gene. By just doing the cross once you won't have to worry about fixing the barring gene which would take multiple generatations to achieve. Also the Wheaten base (recessive) is not able to autosex chicks unless you have a lot of red modifiers because the yellow chick down won't show the barring gene. By doing a one time cross you also won't have to fix the blue egg gene (dominant) or the dark brown egg genes (recessive).
The Crele Penedenseca already have the sex-linked barring gene and already have a the wild type primary color patter. Crossing those hens with a Cream Legbar Cockerel will give you autosexing chicks. You could breed them forward to work on egg color without having to worry about the auto-sexing. Olive Egger projects typically separate eggs into two batches when hatching so that all the eggs that are really light in color can be breed back to pure penedenseca and all the really dark eggs can be bred back to pure legbars. The colors can be improved over a few generations to get to what you want. Again, you could just do hybirds with the Penedenseca too. It keep you from losing the blue egg gene or from losing dark egg genes.
