There is no per page or per line tagging, only per document.
My sense/advice is nevertheless that for someone who has manual workflows/practices like what you describe it has a good chance of working for you, but it is a different tool than paper and pen and you will need to figure out an adapted workflow that is probably different than you are expecting. For me it took a few months, and a few iterations, to arrive at the eventual solution.
I write on the order of 50+ pages a week of unstructured and semi structured notes and usually go back over them 2 or 3 times to extract and reprocess. It would be nice of course to have OCR or search or more structural or UI support, or any number of things that in theory can be available from a digital device.
But the RM is a narrowly focused tool. It is a great writing experience, and it is extremely low power consumption so it has very long battery life. I appreciate and agree with those tradeoffs and in that context find it extremely valuable, essential and nearly irreplaceable, despite its limitations. And my use of it is now very different than was my use of paper.
Yeah. I do a few different things. I do sometimes "tag" with a notation in the left margin but the digital format allows for other techniques. One example- I arrived at using a single "document" per week, and then using a "pattern" of pages within a document for structure. Each day I create two or three pages, the first for the start of unstructured notes, then one or two distinct summary pages, depending on the work.
When writing unstructured notes, when getting to the end of a page, it is easy to insert a new page to continue the notes. But since the summary pages immediately follow the current unstructured page, I can also just flip ahead one or two pages to capture something specific on the appropriate summary page, when it comes up, and then flip back to continue notes.
I also keep a weekly summary-type page as the "last" page in the document, and it is easy to jump ahead there as well.
I used to use Levenger Circa notebooks and would add and remove and move pages around, but digitally it is much more fluid.
Hope that makes sense- it just an example of the sort of behavior mnemonics that are available with a digital tool. I sort of had to go through the process of trial and error to understand how my brain wanted to structure things given these new affordances. And different things work for different people.
Something that a lot of people like on the RM and I don't are page scaling and scrolling. If I could turn them off, I would, but there does not seem to be a way to. And a lot of people find them valuable.