Just curious if “number of panels” is a genuine metric by which financial terminals are judged?

The only real metric by which financial terminals are judged is "Why don't we have any bloombergs? The bond traders are throwing a hissy fit."

Panel is an arbitrary UX delimiter, so fundamentally no, unless you're really pedantic in defining (upfront) panel as a meaningfully semantic unit across apps.

Not really. The quality of data and latency are paramount, that's what you are actually paying for.

Surely it gets noisy after 30 or so, but pedestrian stock trading apps like Thinkorswim have very high levels of customizability and modularity. I think even extensibility in Thinkorswim’s case. Java I think. Anyway, I would think any users of OP’s app are not using 90% of the 500+ widgets.