Yes, I had hit this wall a while back, before I started using the Vocab feature here on Bunpro. Wanikani vocab – whose main purpose is not actually to learn a lot of vocab, but simply to help with learning kanji – was/is not really enough to get one to a decent reading level.
Quite simply, I just started doing a bunch of Learn sessions on Bunpro’s Vocab, starting on N5, then N4 – a large proportion of which I had already learned either from WaniKani, from Bunpro grammar points, or just from exposure to Japanese in other media, so I was able to breeze through these levels pretty swiftly – and finally N3, where I’ve finally hit the point where I’ve had to slow down significantly on Vocab and just give myself enough time to do the Reviews and let the SRS sort things out for me again.
When doing Reviews, I’ve been doing the combined “Grammar & Vocab” aka “All Reviews” sessions. This means that all reviews are treated equally by the SRS system, so they are only sorted by SRS level, and are otherwise just mixed in proportion. And since I’ve added so many Vocabs, and most of it is still in Beginner and Adept SRS levels, now my progression is no longer ‘limited’ by Grammar, but by Vocab. Which is as I want it because Vocab has been my biggest deficit for a while and is only now starting to catch up by ‘filling in the blanks’ I was missing.
Only ‘hold off’ – or merely just ‘slow down’ – on doing new Learn sessions for Grammar. Don’t stop doing grammar Reviews. Just do the mixed “Grammar & Vocab” aka “All Reviews”. This will automatically pace your grammar reviews in proportion to the amount of vocab you have added to your review queue (via Learn sessions on vocab).
Although there is a lot of Vocab for N5, much of it is pretty easy, and you’ll already have had exposure to much of it, too.
Also, and importantly, I would recommend using the “Fill In / Manual” review type for all the vocab for which that style of review is available (currently only N5 to N3, but N2 is coming relatively soon-ish, also). This style of review is much closer to the typical grammar review style, with a Japanese context sentence with blanks for vocab (so-called ‘Cloze’ style review), and optional hints and English translation. You have to enter the Japanese kana, and it converts to kanji (if apporpriate).
This contrasts with the typical vocab review style you get on most other platforms where you are shown the vocab directly in Japanese and need to produce the ‘translation’ in English. In Bunpro, this style of review is called “Translate / Manual” or “Translate / Reveal & Grade”.
A big benefit of the “Fill In / Manual” style is that you can use the example sentences as practice for reading. In the process, you will naturally be practising your kanji meaning- and reading-recall (say from WaniKani), as well as grammar structures, as well as picking up additional context-vocab along the way.
This alone should address your main concern that the example sentences (for grammar) are already too hard to read consistently. You’ll get lots of practice reading sentences just from the vocab sentences from N5 and N4. (I also use auto-playback so I can hear the sentences read aloud after I give a correct answer, for listening practice.)
A secondary effect (though important IMO, although I understand it may not be so important for other folks) of doing the “Fill In / Manual” style of review is that you get practice with typing the Japanese for each vocab, giving you lots of experience with so-called ‘production’ (bringing to mind how to say/write it) and specifically with using the keyboard to type the words. If you ever want to be communicating in Japanese in writing (say, in typical online comments or whatnot), then you’ll need to get practice doing it somehow, and I find that these vocab reviews give plenty of practice!
I recommend instead just following the JLPT level ordering. For each ‘official’ Bunpro JLPT deck, e.g. N5 Vocab, you can (probably should) set the ordering to something useful like Anime or Novels or General. The default Alphabetical is pretty well useless (and boring as hell) in my opinion. I chose Anime, for example.
It doesn’t make a big difference which ordering you choose. The main point is that you’ll be learning all of the common/important/useful words first (or at least early), and this will help tremendously to ‘fill in the gaps’ of vocab that you are missing.
Maybe at the very beginning, you’ll be learning items that are just so common that you already know them. Don’t worry. Just zip through them as quickly as you like. Since you know them, they will quickly advance up the SRS levels and in ‘no time’, you’ll advance them to Mastered. But while you’re doing this, you’ll be getting lots of experience and practice with seeing the vocab in context, as well as practice reading sentences with other words/vocab and grammar, as well as practice typing, etc.
If it’s ‘too easy’, just zoom through it until you get to some words that are less familiar. These are the ‘gap’ words that you need and are currently missing, which will make reading more advanced sentences that much easier, since they’ll take far less mental effort, and you can focus your efforts on the new/unfamiliar vocab in these sentences.
So, yes, I would recommend just starting on the N5 deck, ordering it by something useful like Anime, or Novels, or General, and then zipping through it until vocabs become the majority of your reviews for a while, until you ‘catch up’ to N4 vocab to match your N4 grammar, and then skip ahead to N3 vocab as it suits you, etc.
If it’s easy, it’s easy and little effort, just do them. (Heck, even enjoy them, since they are so easy to succeed at!) If it’s not easy, then great!, those are the vocabs you want to learn anyway, to ‘fill in the gaps’ in your missing vocabulary.
Oh, by the way, if, in this process, you come across vocabs that you have to ‘learn’, but you really really already know and don’t want to practice with reading example sentences, and typing, etc., then you can easily ‘Mark As Mastered’, and just like that you won’t have to review that vocab ever again.
So, there really is no reason (IMHO) not to go through the N5 deck in some useful ordering (as I said, like Anime, or General, or whatever), to fill in the gaps. At least, in terms of using SRS to study. Lots of folks will say that they find it better to just go out and read Japanese in the wild and you’ll naturally pick up vocab along the way. Whatever works for you. I’m just talking about how to use the BP Vocab SRS system in conjunction with their Grammar SRS system. (Well, I guess actually they are the same system now! Haha 
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