You can scale up, sure. I usually aim for an 850g loaf (pre-bake, so dough weight) and make 2-3 loaves at once. I still bake with the lid on for 10-13 minutes, remove lid, and then bake til done, whenever that is.

I have a Tojiro bread slicer that I love. I don't think you'll need a "bread holder" if you upgrade your knife. But be careful, it's going to be incredibly sharp.

Alternatively, Tojiro DP Gyuto and Petty.

And whether you decide for ST or Tojiro, add this Tojiro bread knife.

Edit: corrected the Amazon links to not contain any referrals. Also, while doing this, I realized Amazon autotranslate to German makes Petty knife into Kleintiermesser. Which is a knife you'd use to butcher your hamster of fillet your goldfish.

Try this first: https://www.amazon.com/Tojiro-Bread-Slicer-235mm-F-737/dp/B001TPA816/

It might be a bit too flexible for your use case, but it's a great knife at a great price, so... you won't regret buying it.

And yeah, serrated knives are, IMHO, like non-stick pans. Don't spend too much on them, because they can't practically be sharpened.