The idea of "build the barn first before adding the paint" was not as literal as you thought...although that was a good thing too.
Old-timers refer to building the barn before adding the paint as a reference to getting the type set on your birds before focusing on the color traits. Anytime a new bloodline is brought into the mix, there will be characteristics that surface that need attention. Often, color will hit the focus on the F2 or F3 generations.
They also recommend breeding a separate line for males and another for females. The male line often produces the best show females and the female line produces the best show cockerels.
I have a closed flock of Columbian Wyandotte and know exactly what you mean by "not doing a sprint in my breeding plan I am doing a marathon".
I have had my flock now for 5 years, the owner before me for 5 or 6 years and the owner before him, retired after many years with the bloodline. A side breeding of a Blue hen with good type and leg color with a select cock had nice effect, but brought a few comb issues that needed to be corrected, This year I have another side pen using a White Wyandotte cock with the Columbian hens to strengthen the leg color, good combs, and greater size. The original pen bloodline has been kept "clean" until I feel I have a good line to strengthen the original flock.
Tell us about your birds.
First priority in my flock is health and vigor, followed by utilities, followed by the breed standard. There is no cut and dry way to determine which bird has the best vigor but we watch to see who is the fist off the roost in the morning, who is the last to the coop at night. Who is busy foraging in the heat of the day and who is sitting in the coop by the food bucket all day. We also look at the conditioning of the bird. We also look at how the bird moves. I look for cockerel that strut on walking on the tips of their toes as opposed to ones that walk flat footed. I watch where they hold their wings. Cockerels that hold these wings high and well tucked up are usable while that they let the wing tips point downward are not. I use the Hogan method, head points, and egg records to determine who the best layers/ quick molter are. I use mature weight, etc.
As for the Breed standard, after I have evaluated the birds for vigor and production I don't always have a lot of choices, but I like to look at the tendency of the flock. If I have a grow out group of 40 birds and only 2-3 meet a certain point in the standard, then I am going to want to keep the best of those 2-3 so that I can keep that trait in my flock. Otherwise the next season I may get 40 and none of them may meet that point in the standard and it may never resurface in my flock. Likewise if there is a defect in my flock that all but 2-3 birds share, then I am going to work with the birds that don't have the defect so that I don't get to where 100% of the flock has the defect and it is locked into the flock. If I don't have any pressing issues to address in my flock I like to start with the ones with the best mature weight and go from top down to find one that has the distinct shape of the breed. Then I look for other defining breed features and color for the variety.
Note: a good friend of mine that I met through breeding chickens traveled from Texas to the North Carolina when Grant Brereton was here from the UK to do a seminar on poultry genetics. He is a poultry judge and published author on breeding standard breed chickens. She commented to me that he felt that some color patterns were more difficult to achieve in chickens that type and that in those varieties he would work on color first then work on type. That was backwards from everything I have learned. If you are breeding White Plymoth Rock, or Black Australorps the order of doing things may be different than if you are breeding a complex colors and patterns. Since I can't eat color I feel that utilities are more important, but to get a well rounded bird I have to keep everything in mind and make sure that I am not breeding out traits early on that I will need in my flock later on to finish it off. Sometimes that means picking the better colored bird over one that is slightly better in other ways. For me it usually boils down to picking the hen with the best type and cockerel with the best color after culling for weakness/defects and narrowing down on the ones with best utilities.
I DON'T breed a separate line for males and females. I realize that some color varieties and some features in the type look stunning on the hen (i.e. the graceful folded over comb of the leghorn hens) but not of the cockerel (i.e. you want erect combs on a cockerel) and visa versa but the idea of a "breed" is to have a homogeneous flock. I measure than by what percentage of the flock is a good representation of the breed standard and what percentage are not (i.e. culls). If you are double mating (i.e. breeding one flock to produce good male specimens and one flock for good female specimens) then yes the quality of the males from the male line can be a lot better than a male from a single bred flock and your females from the female line can be a better specimens than from a single breed flock, but 50% of your female line (the males) are not going to have any potential for exhibition and 50% of your male line (the females) are not going to have any potential for exhibition. I fail to see how less than 50% of the line being a good representation of the standard can improve a "breed". With breeding two good standard birds together to try to achieve good standard birds in both the males and females you have to give up a little bit on the female extreme and a little bit of the male extreme and meet in the middle. That is much harder to do because you have to know what type of female produces what type of male and what type of male produces what type of female rather than just type breeding for a female and not worrying about the other half of the equation or type breeding for a male and not worrying about the other half of the equation but when done right you can get to a much higher percentage of the flock that are coming out as a good representation of the breed (i.e up to 100%). That is going to do a lot more for improving the quality of the breed in my opinion. So... I am not out to breed one super bird while culling 99. I am out to produce 100 birds that are all uniform in vigor, utilities, and breed standards. To me uniformity = quality. One good birds that can't reproduce its quality in a high percentage of it offspring may be nice if you win a big price at a show but is not homogeneous and not what I call quality.
Tell us about your birds.
Hard to tell right now since I got rid of all the proven breeding stock and am starting over again with a small hatch from this spring. The Cream Legbar pullets all started laying at 20-24 weeks this year. I usually don't see eggs until about 23-24 weeks so I was happy about that. In previose year we got some hens that laid a really pale colored blue egg but I haven't seen any of those in this batch yet. Next august's heat will be the test on that.

In Texas we had 12 coops and could separate out the pullets into flocks that laid different colored eggs than them so we could keep a daily laying record. Our first year were had a flock average of 165 eggs in the first year of production. ALL the hens went broody and took time off. One was allowed to hatch a brood and she did a great job as a mother. The 2nd year we had 2-3 pullets in the grow out group go broody but we have only seen one broody Cream Legbar in the past two years, so with less time off the flock average came up to about 180. We know who our top layers are now, but only have flock averages on production numbers, but I know that one hen only was taking a 4-5 week molt and laid like a champ. I am sure that she was laying over 200 eggs and probably closer to 225. Not bad for a flock that is not on lights during the winter and not managed for breeding rather than production. Most of my original hens laid an egg in the range of 60-62 grams. We had one hen that laid an eggs in the range of 67-70 grams. We selected for egg size in her offspring. Only about 1 out of 10 of her daughters were laying the 70 gram eggs. We breed those 70 gram egg hens and were up to 3 out of 4 hens from that line laying bigger eggs. The pullets right now are laying between 45-60 grams eggs. I am hoping that in March and April to see some eggs in the 67+ range but only had two pullets from that line and a preditor took one of them a few weeks ago so I am not sure what we will see. We did breed one of the cockerels from that line to another line this spring for one of the the breeding groups, but like I said it is hard to know what we will see. We like our flock. We have a not of defects and type issues. We culled for hen spurs, greed dermal spots on the shanks, insufficient white coloring on the ear lobes, small crest (and not crested all together), pale leg color, squirrel tail, narrow bodies, etc. We have seen progress and are happy that the line is starting to settle. So main goals Big birds, 200+ eggs production, 70 gram eggs, good type, good color. good disposition.