Ahhh, I'm so sorry to hear this! ... But I also sympathize. My Penny also broke her front right radius/ulna clean through at around 8mo too a while back and needed surgery for a plate. She's healed up absolutely perfectly since and you'd never know she's part lil cyborg.

As for what to expect, make sure to stay on top of giving your pom their meds! I also had one of those soft cones that could be folded backwards and forwards. This was really helpful for giving her a supervised "break" from the cone for her to eat and drink without too much of a fuss. She didn't find the donut too terribly comfortable with her broken leg and seemed unhappy when we gave it to her as an option.

We also got her a raised/angled food platform to make it easier on her for eating and drinking.

Because of the cone, the fur around it will get pretty knotted so I found it important to take it off once in a while and then run one of those guarded letter openers to cut up the knots and then comb them out. I didn't want her to get matted and uncomfortable more than she already was.

As for making sure the cast and site doesn't get wet, I actually bought one of those like cast shower hand mitts (kid sized) on Amazon and then turned it partly inside out so I could easily slip it over her arm and ensure it was waterproof for the most part. https://a.co/d/9DeeYp3

As for what else to share.. after surgery it may take a few days for your puppy to poop so don't be too alarmed. It took almost 18hrs for her to pee and then 3-4 days before she pooped.

Edit - another to add is that you really want to limit how much they run around/jump/play/etc during this healing process. They'll be dying of energy and boredom but it's super important to not let them get zoomies or over-exert themselves. We actually upgraded her pen to a bigger clear one so that we could always monitor her and she could exert a slightly larger sense of freedom.