You can just study vocab with Kana<->English alone. Personally, I focus on English->Kana.
Relying on knowledge of On and Kun reading of some Kanji, Level 16 might be a good place (all JLPT N5 kanji).
Relying on vocab knowledge from WaniKani alone, I feel that Level 20-30 is a good place (2k-3k vocab, as WaniKani has 6k vocab).
At some point, you’ll need Kana vocab beyond passive learning anyway, like Onomatopeia. You’ll have to actively memorize it. Also, sometimes vocab have rare Kanji; you don’t have to wait to learn it.
I know that Anki or Memrise might be trouble. Why don’t you try Houhou 1.2 - Dictionary and SRS application for Windows?