I have read your posts, and do understand what you are trying to accomplish. Would you consider buying bantam chicks from a feed store? This way, all would be same age, as they grow. No issues with introduction of different age chicks together.
Your way of getting a hen, and breeding with your rooster, does pose some situations. Bantams are not as prolific layers of eggs like,, compared to production hens that produce an egg most days. 4 of my 6 chickens are banties.
You may have to wait some time to collect enough eggs to incubate at one time. Not sure how many eggs you would get in 2 weeks? Eggs older than 2 weeks, and hatch-ability slides downhill.
Also consider that 50% can turn out less desirable cockerels. Same is true with straight run from store. Do you have a way to relocate chicks that you would not want to keep??
You are in a totally different area from me, so not sure offers such as these for me are available in your area?
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The hatcheries that I checked all seem to offer bantams about the end of April.
If you would be able to check with a feed store in your area, maybe that would be an option for you to take.

Maybe the feed store would carry some bantams at that time, and you would not need to order the larger amounts??
I also recall that you intend to be a future vet. Would you be able to vent-sex the chicks to pick out your choice?? I know that wing sexing needs to be slightly older chick.
Is Craig's' List a possibility for chicks in your close vicinity??
WISHING YOU BEST,,,,,,,,,,,,,,,,,,,,,