That’s just it, right there. You actually have full control over your own pace – well, with the slight exception that if/when you change your pace, your currently-already-scheduled reviews will still remain scheduled at their current times/dates, so it will take some lag time before the number of reviews you get on a daily basis slows down to match the number of new lessons you do each day (or week, for instance).
But if you just keep going at a comfortable pace – checking-in with yourself briefly each day, like, “How was that amount of reviews today? Too many / overwhelming? Too few?” – and adjust your lessons accordingly, then pretty soon the SRS system will settle in on your pacing and you can keep that comfortable pace going as long as you like.
Now, whether the actual difficulty of the kanji might require you to slow down on lessons or not – well, almost certainly after a few levels more, you’ll start getting back items at the Master and Enlightened level, and as that number of reviews increases, you’ll have to slow down a bit if you want to maintain your current comfort level. But, once you get past a certain point, even those reviews will balance out, and it will become more of a steady load for the remaining levels.
As for higher WK levels, the kanji do become more difficult and may require slowing down for that reason also. But on the other hand, you also kind of ‘learn how to learn kanji’ more, so in a way the entire process becomes ‘easier’ in a certain sense. Once again, if you just maintain a comfortable lesson/review load on a day to day basis, the SRS will balance out over time, so it should be sustainable all the way through.
However, many people (myself included when I first started) try to sustain a rather high load for a while, and then eventually when they (for example) have to take a break for whatever reason, when they come back they find a giant stack of reviews, and that can be really daunting and lead to burn-out. But again, it’s usually because of trying to maintain too high of a pace for a while and not slowing down to a more comfortable/sustainable pace.
If you ever do get to that point of being overwhelmed, you can just slow down and eventually the system will sort itself out. I ended up doing that, and there’s even a group thread for folks who choose to take things slower: 
Let’s Durtle the Scenic Route 