I know the reasoning for not mixing LF and bantam, but want to share my experience.
I brood everything together. LF, bantam, ducks and turkeys. Of course the ducks after about 2 weeks are so messy and big they get seperated until they go out side. I have several brooders and they are seperated by size of the bird rather than breed. When its time to go out side all go to the bantam coop. As the LF, turkey, and duck out grow the bantam they move to the barn. Now there is exceptions to that. I have a 3 month old duck who thinks she is a Silkie and has 4 5 month old Silkie siblings. At this point she is twice their size, but don't tell her that. They sleep in one big pile on the floor. I also have 6 week old turkeys in with older silkies.
Now as adults they stay separated and go their separate ways when free ranging. The exception to this is Aunt Bea a EE. She thinks she is a Seabright. When I tried to move her she flipped out and did not understand why I was putting her in with the giant birds. As soon as I opened the barn she would run to the bantam coop and try to get in. For a week I would find her asleep up against the outside wall of the coop run and Sally Seabright would be up against the inside. Both were stressed and loosing weight so I let her back in and all was well. She doesn't pick on any of the bantam, but then again she thinks she is a Seabright. LOL.