I don’t know, 83 days is plenty long, although not in the scope of how long you’ll spend studying Japanese. But welcome to the WaniKani forums! 
- It depends on your accuracy and your pace. Anyway, no, it generally doesn’t get worse, since for most of the levels the amount of vocab is the same, as far as I can tell. If I’m wrong, someone please correct me orz.
Good idea on stopping to do your lessons. I recommend slowing your levelling pace to keep up with vocab in general, as the vocab lessons will reinforce your knowledge of readings, teach you new readings, and most importantly are things you need to know for reading the Japanese language. They are meant to be done together. Additionally, if you always have to do your vocab in big bursts, they’ll keep coming to haunt you in huge spikes for your Master, Enlightened, and Burn reviews.
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Burn reviews will increase your workload to the final maximum in the exact same way Enlightened and Master reviews did, and any mistakes will move those down into the lower piles, but that’s about it. Some of the much later levels are faster in a way I don’t fully understand, so I can’t account for those. Sorry D: I do all my vocab lessons as I level and always have 0 lessons before I level. However, there are a number of days I do 30 lessons. So my queue is 100 +/- like 40.
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I think challenging yourself with interesting manga etc. is important, but so is reading things at your level and just improving your reading speed. Try reading NHK News Easy articles, or graded readers, or short stories and folktales. I use all of these and find them very helpful, as it’s more efficient than studying through reading manga, but I find the harder texts more interesting and memorable in their own way so I try to do those too. The Ultimate Additional Japanese Resources List!
There are reading groups on the forum you could join too. The beginner club is voting right now (they will probably pick a book), and there’s also a lower level beginner club forming to read a grade school level text at a page a day. The advantage is doing it in a group for motivation and to be able to get help with things you don’t understand.
You might find this an interesting tool: Wanikani Statistics Plug in your API key and how many lessons you do a day (or want to do a day, you can just keep tweaking it), and it’ll give you an estimate of your apprentice queue and how much work you’ve got to do in reviews to maintain it based off your accuracy (and some other assumptions, see: Choosing the right pace for your lessons (thanks to queueing theory)). So it’s an approximation but still interesting.