Banneton size/ dough weight/ volume for new cast iron.

Hi all!

I just joined, so it's good to meet everyone!

I just got this cast iron roaster:

https://www.bayouclassic.com/products/5-5-qt-oval-roaster?_pos=1&_sid=85e48f5b2&_ss=r

I'm trying to figure out what size banneton (and how much dough) I should use to nicely fill the roaster without leaving much space. It's dimensions:

12.125" long

9.25" wide

4.25" high (lid off)

7.5" high (lid on)

I know it depends greatly on how open a crumb I want, so to give you a better idea, I'd like to use this recipe:

https://cotswoldflour.com/blogs/bread/heritage-wholegrain-sourdough

Thoughts?

Thanks in advance!!  :)