Regarding 2.: Most of these objects do not directly correspond to rendered elements. Basically every page has one (typically) content stream which will contain all rendered elements. The biggest rendered thing you see outside of that are annotations (link boxes, form fields, actual annotations, ...).
It's a bit different if you are looking at a tagged PDF, where the tagging structure is in there, but if you want to look at that in detail you are probably better served with e.g. ngPDF (https://ngpdf.com/) which will show the tagging structure including the mapping to rendered elements.
It's a bit different if you are looking at a tagged PDF, where the tagging structure is in there, but if you want to look at that in detail you are probably better served with e.g. ngPDF (https://ngpdf.com/) which will show the tagging structure including the mapping to rendered elements.