Do you have examples of words? All words in the JMDict (which is used by most online Japanese dictionaries) should get recognized unless the reader has trouble splitting the words correctly. Names and such will not be recognized however.
Regarding JLPT levels, these are actually show on both the vocab and the kanji popups:
It also shows the frequency of a word in the full text, so in the above screenshot the vocabulary appears 14 times (in any inflected form).
Kanji cards do have the JLPT Information included upon generating, but I just noticed that the vocabulary cards do not (as you mentioned). I’ll change it so it adds that to the notes field
This is something that has come up a few times before, but would need a serious rewrite of the internal system and would break the current UI regarding srs ranks/intervals. So in that regard it’s been fairly low priority for me as I think the current amount of intervals suit most people’s needs.
Good question! I think it’s more about what your pc can handle as it transfers all card data to your browser when opening the cards management page. If it’s too many it can cause your computer to run out of memory and freeze the browser.
There are decks with over 20-30k cards in them that seem to work fine, but in general I’d advise you to keep it to less than 10k cards in a deck, if only because it keeps the card management page loading as fast as possible.
You could also just consider splitting a deck into multiple or starting a new deck after a certain date (like 2022 / 2023 etc).