WK only requires you to complete 90% of a level’s kanji in order to level up. Vocab isn’t considered at all. I’ll generally do 5 radicals/kanji + 5-10 vocab or else just vocab when I’m doing lessons, and the vocab I’ll just choose pretty much randomly. I’ll try to avoid any that have overlapping kanji since I find it easier not to have them all lumped together, and I’ll prioritize words I’m less familiar with.
The number of items you have at each stage depends both on how quickly you go through lessons and how often you get things wrong. When you get an item wrong, it can get knocked down one or more SRS levels, even falling into a lower stage. I personally pay little to no attention to how many I have in guru, but apprentice I’ll generally keep below 100 (though it’s currently hovering around 40-50).
The number of lessons you do should also depend on how much time you want/are able to devote to WK. You say you want to start reading soon, and that depends more on your grasp of grammar and your tolerance for unknowns and lookups than on WK level. If you haven’t started grammar yet, you may want to do that soon and possibly slow down on WK a bit so you’ll have some time to devote to that—and maybe even slow down further to carve out some time for reading. It all depends on the balance you want between your different methods of studying and engaging with the language.
I’m currently doing WK lessons sporadically but still doing reviews every day. Most of my JP time is spent reading and some of it listening. (Grammar I’m back to hoping I can just absorb it through osmosis. I’m allergic to textbooks and SRSing grammar is far more frustrating than anything for me. I’m not sure how well it’s working out tbh, but even if there are sentences I have to read more than once, my understanding still seems to be generally not bad, so? I’m pretty okay with it at present.)
My advice, when you start reading, is to let your interest guide you. When I started out, I picked the 番外編 short story collection of a series I loved and very slowly—like, 2 to maybe 6 pages a day slowly—read the third story over the course of a month. I picked up manga I thought I would like and read 1 or maybe 2 chapters in a day because that’s all I had time and stamina for. And I had a better time of that than when I tried to make myself read graded readers because I thought I “had” to because “everyone” read those early on. Sure, the language is easier in them, but so are the stories, and they mostly didn’t appeal to me.
If you find a book that a WK book club has already read that you’re interested in, you can read through the threads corresponding to each section of the book because along with their thoughts on the story, people will also ask questions about the language, etc. If there’s something you’re struggling with, it may be that someone else has already asked and gotten an answer—and if not, you’re completely welcome to ask yourself. Many readers still follow the old book club threads and are happy to help.
The website Learn Natively may also be of use in finding content or deciding which order to try reading them in. The way it works is that users will grade different books etc. against each other to get a relative difficulty level for them. E.g. something like よつばと! is going to be in the mid- to upper teens, sports shounen manga are generally low to mid-twenties, LNs often hover around L30, and it’s not unusual for more literary works to reach the 40s. And it includes both native content and learner-oriented content, and users are able to rate them and leave reviews. So you can find things that both you think you’ll enjoy and are around your level. (People on there seem to love to claim that a book has no furigana when really it’s partial furigana though, so don’t put too much stock into that.)
Also, don’t be afraid to just dive in if you find something you want to read. You can always put it down if it’s too hard, and now you’ve got a better idea of where you stand and where you need to get to than if you hadn’t tried at all.
