I’m not going to say that all of the words found on the BunPro decks are must know, but most of them are very useful (especially because they also appear on the grammar questions during reviews). について is definitely a must know word, IMO. It means “about”. Yes, it is also an N3 grammar point, but if your goal is to learn Japanese then why worry about what level it belongs to? Just learn the words.
Even if your goal is to pass the JLPT N5, there are no cut and dry vocabulary/kanji/grammar decks because the tests are different every year, and you will see some words/grammar points from higher levels show up on the test anyway. It is inevitable since they need new content. All of these graded decks are just estimates. That’s why it’s a good idea to learn a little bit above the level you want to test on.
My suggestion is to learn as many words as you can, regardless of their level, as long as it’s not some rarely used word (at least for now, until you get to higher levels). And if you’re confortable reading hiragana and katakana, learning Kanji will help memorize words even faster since there are many words that sound the same but mean completely different things which, besides context, kanji will help differentiate. Also, once you learn the meaning and reading of Kanji you will be able to read and guess the meaning of Kanji you’ve never seen before. It’s not always the case since there are times when Kanji seems random, or have readings that are exceptions, but it’s an awesome feeling when you get the reading and/or the meaning right. Not to mention, you’ll need to know how to read Kanji anyway. It’s inevitable.
As for what to use, besides the BunPro decks (which I think are excellent), there are those from Anki, Memrise, etc. Both have tons of decks based on JLPT level, commonly used words, books, etc. As for learning Kanji, my favorite method is WaniKani. I personally don’t think there’s a better way, but that’s just me. As long as you’re learning them in the context of words in a sentence, rather than in a vacuum (which is the worst way to learn Kanji), you should be fine. I’m sure others will chime in with their preferred method to learn vocabulary. Check them all out and see what works for you. At the end of the day, it has to be something that works for you.
HTH!