What interaction would trigger this? I was guessing you wanted it to be a URL?
The DOM is constructed when the document is created. Properties/Attributes are assigned when the scene is loaded. There's no Hype distinction for items coming into view, though undoubtedly browsers optimize rendering paths when items are hidden or offscreen.
The recommendation is more based on the fact that over 50 scenes is difficult to manage in Hype's UI (since there's no scene grouping, filtering, or multiple selection ) and also that at some point there's going to be a lot of overhead even if they are all empty scenes.
As for elements, at least you can group them or use symbols . There's no hard limit, but everything has a cost. I think it is more your call in what you're comfortable with and how frequently you may need/want to reorganize. There's other things to consider; generally re-render performance of SVGs is much poorer than raster formats, so it could be that N elements is terrible with SVGs but completely fine with other elements.
This is a browser implementation detail; the general answer is "yes" but is highly depending on your document and what you're doing.