When I had the Bianca my recipe was almost always 19g in 38g out, for the coffee I enjoy (South American blends, med-dark roast) it was typically between 28-32 seconds. I didn’t ever change boiler temp, pre-infusion or pressure.
It’s SO easy to overwhelm yourself with the seemingly ever-growing list of tools and methods and variables here so my advice would be to go right back to basics and just get a consistent coffee you enjoy. That’s the goal, after all.
Lighter roasts and single origins can be a massive pain to dial in. I’ve been making espresso at home for over 10 years and I still avoid ultra light roasts because so much of it goes down the drain while trying to dial in. Then you spend £14 on 225g and get one enjoyable coffee from it.
Cuprajake’s North Star is a great suggestion, Rave Chatswood is a similarly priced coffee that is also very forgiving.
Leave the paddle fully open, don’t touch it. It will confuse things until you can get a decent shot without it.
Try using the spouted PF, yes it will mask any channeling but again, for now, the goal here is something repeatable that tastes good. I’m not saying channeling isn’t a bad thing, but if it tastes good, who cares.
19g in, don’t WDT, just give the PF a tap on the side until the bed of coffee looks roughly even, then tamp, quite firmly.
Dial the grind until you’re getting around 30 seconds with the above and then taste. I’m not saying every Brazilian coffee tastes great at 1:2 at 30 seconds but I’m yet to come across one that tastes bad with that recipe.