I aim to keep dashboards no larger than what can be displayed in a single window on a desktop, with perhaps some supplementary plots below, often in a collapsed row. I make heavy use of "drill-down" links, preferably from tables or single-stats (or more often the "status panel" for denser displays [1]), or in panel notes otherwise, to dive further into the data.
When designing a dashboard, I ask myself "what story is this dashboard going to tell?", and as with a good novel I try to keep from straying too far from that narrative, branching side-plots out into new dashboards as needed.
> show me everything so I can see at a glance
Yes, exactly, at a glance, not after scrolling through five pages. With careful dashboard design, you should be able to see a problem area actually "at a glance," and then drill-down to pinpoint the actual cause, faster than you'll find it scrolling through a single large dashboard.
I admit this is something of an ideal to aim for, and it can take a lot of time and effort to achieve, which may not be available. However, it will pay off in the "Oh my god something is wrong in production right now" scenario if you can take that time.
Scrolling through 100 graphs is slower than scanning 10 main graphs and 10 subgraphs per.