Thanks for the questions.
Currently, it’s not possible to change the text size. Be sure to check the scale of your print to make sure you’re maximising the space available and the size of the text.
Regarding getting the barrel number on the labels, if you print your labels directly from the racking process (rather than ‘Print labels pre-packaging’ or printing via ‘planned packagings’), you should see the container code on the labels. Once you complete a racking, you should see a button to print labels. As the racking is directly connected to the containers themselves, you’ll see the container code on the labels. If you need to print these at a later time, go to the batch in question, then to the ‘Actions’ tab, then click the little print icon next to a racking line.
There’s a feature request thread, here, for more customisation on product labels, so it might be worth giving that a vote and adding any other ideas you may have.
I hope this helps.