I would skip the bread, and just give the starter with supplemental egg.So, for the first ten days we have starter first age. However unlike the recommendation I see here it's around 12 % protein. I'll do with that and I expect my partner will add the mixture of boiled egg and bread the first days.
( BTW I think one of the main problem, beside salt, with today's bread is the leavening agent, most of the time baking yeast instead of sourdough. I'll make sure we get sourdough bread).
If you can get the high protein end, I would just feed that from the very first day, and not bother with egg, or two kinds of feed.Then, I find an other type of food called either second age, or pullets/cockerels. Now depending on the brand it ranges from 12 % to 21% ( that last one is professional range). That's a huge gap and most of the brands that are easy to find are rather on the low spectrum.
Mixing a higher-protein feed with a lower-protein feed can also work. Depending on the proportions you use, you can get any protein level in between the two starting points.
I would use the second stage food, or the all flock, and skip the layer. Just make sure they have a source of calcium (like a dish of oyster shell) so the hens can eat what they need. The chicks may sample the oyster shell too, but they typically don't eat enough to cause themselves any problems.I would like and will have to integrate the little ones as soon as possible with the actual flock, hopefully between two and three weeks. That is, if we don't have too much aggression seen how they all absolutely hate broody Chipie. So this means the same food for everyone. Now I understand layer food with 3 to 4 percent calcium would be harmful for growing pullets and cockerels. Should I put everyone on this second age feed thing and try to find one with higher protein content ? Or go with "all flock", that in my country has about 14 % protein ? Or do a mix of layer and all flock ?
My understanding is that US chickens foods have more protein than the chickens really need, but just barely enough of certain amino acids. The rest of the protein is extra of some amino acids, which does not harm the chickens but does not help either. If your country is being more careful about the balance of amino acids, the chickens may get just as much protein they can actually use, even with the total protein being lower.
@U_Stormcrow knows more than I do about the amino acid requirements and reading labels, so he might be able to help you check the foods that are available to you.