I would not build that many nestboxes into the coop.
Bantams are typically happy to use the same nestboxes as bigger chickens.
A common estimate is one nestbox for each 3-5 hens. So for 9 hens, 2 or 3 nestboxes are usually enough.
Hens usually like to use the same nestbox as other hens, so they will probably all lay their eggs in one favorite nestbox, and maybe a second or third if several need to lay at once.
The one exception is if hens go broody. Each broody hen does best with a nestbox of her own for as long as she's broody, but even if every hen goes broody at the same time, you won't need MORE nestboxes than hens.