It sounds like you have a pretty good idea of the SRS intervals, and have chosen one of the two most popular schedules for hitting them on time. Your post makes me think you’ve probably already read this, haha, but just in case you haven’t, have you taken a look at the ultimate guide to WK? There are lots of tips in there for building a schedule that lets you accomplish your goals.
I think it’s definitely a very good idea to get through your vocab backlog before proceeding further. I absolutely agree that it’s wise to stop focusing on the optimum way to get to the next level and instead focus on a regular, sustainable schedule. WK is very much a marathon and not a sprint, even at full speed.
If you’re worried about your vocab lessons getting out of balance again, one trick that works pretty well for me is using the lesson filter script and aiming for a 1:3 ratio of kanji to vocab lessons every day (since there are roughly three times as many vocab lessons as there are kanji in WK). For me, this looks like 3 kanji and 9 vocab a day (for the radicals, I just do them all on my first day on a level, and if there are more than ten, I don’t do any other lessons on top of them). For 20 lessons a day, you could do 5 kanji and 15 vocab each day. If you do this, you shouldn’t fall too far behind on vocab.
Or if 20 a day is too much (especially keeping in mind that it gets to be quite a lot more work once your master and enlightened reviews start coming in on top of the guru and apprentice), you could do fewer. 12 a day means I level up once every 12-15 days, depending on how many items are in a level. But the pace is extremely doable, and I haven’t felt anything close to burnout. A happy medium might be 16 lessons a day (4 kanji and 12 vocab) if you want a slightly faster pace.
You definitely have some options, and it sounds like you’re on the right track with trying to confront these problems before they become real issues!