In the main comment on this, I explained that I was unburning Radicals separately especially from ‘future’ levels. For example, Radicals from level 10 at the same time as Kanji from level 9 at the same time as Vocab from level 8. But still, Radicals, Kanji, and Vocab all at the same time, all in a mix, just from different levels (especially so that I would get Kanji before the Vocabs they were in, to simulate WK’s ‘unlocking’ mechanic).
Perhaps I wasn’t very clear on why I was doing it this way, but I only started doing it this way after I had ‘ramped up’ the unburning to the point where I was unburning more items than I was doing new WK lessons for. This was because I wanted to ‘catch up’ to my regular level progression, and I was much further ahead at the time.
So I wanted to unburn quite a few items at a time, so it made sense to do the Radicals 2 levels ahead of the Vocabs, so that I would end up with a nice mix of Radicals, Kanji, and Vocabs. I also found it a bit … boring, I guess? … to unburn all the Radicals from a single level all at once. Perhaps I didn’t make this point clearly enough.
Initially, levels 1, 2, and 3-ish, I was more or less unburning items at random. I only started to separate out Radicals from Kanji when Kanji would refer to Radicals I couldn’t quite remember.
It was only later I decided, “Well, I don’t really care to selectively unburn specific radicals based on which kanji I’ve unburned. I’ll just unburn them all.” The reason I was okay with that decision by that time was because I realized I was enjoying the experience of ‘revisiting old friends’, including as a way to help with the pacing of my regular WK progression. Remember, I’m not going for speed or efficiency. I’m Durtling the Scenic Route.
I think this whole technique probably works best when Radicals (in particular) are only mixed in with Kanji and Vocab. Level 1 is a bit of a special case because the radicals are so simple and common, and they’ll feel like they are hindering you from unburning kanji and vocab, which are the meat of what we’re trying to learn in the first place.
So, I’d say that for levels 1 to 3-ish, go ahead and start unburning kanji (especially) and also vocab. It’s probably better to get a variety of things unburned initially, so it doesn’t feel like a chore. Unburn the radicals too, at some point, but they don’t need to be done all at once in a big block.
In fact, maybe I should have included more of the idea that I used some kind of ‘randomization’ of selecting which items to unburn within a particular level. For example, suppose I wanted to unburn 5 Kanji from level 8. I would go to the Level 8 page and more or less randomly pick 5 burned items from the list of Kanji, and I wouldn’t even pay attention to which ones they were.
This gave the whole process a sense of ‘surprise’ (as ‘artificial’ as it was), so that when the items showed up in review I would be seeing ‘something new’ again. Kept the interest and enjoyment up.
Also, finally, of course at the beginning SRS levels, reviews are going to be a bit repetitive. Just zoom through them. As the items progress and the delays between them grow, they will get mixed in with all your other reviews, including future items you’ll unburn at lower SRS levels.
TL;DR: I’d say go ahead and start unburning Kanji and Vocab also from levels 1 to 3-ish. And, pretty much at random, too. Eventually you’ll pick up all the Radicals – just by the mere fact of ‘clearing’ the whole level – but it’s not important to do them all strictly before doing Kanji or Vocab.