For reading, immersion is less about kanji knowledge and more about grammar and vocabulary.
The Absolute Beginner’s Book Club has furigana so knowing kanji isn’t that much of an issue, though it’s recommended your grammar is about N5 level and knowing some kana words will help. Here’s ChristopherFritz’s guide to joining so you can check for yourself how ready you are.
If that seems a bit too much for you, you can also try the free Tadoku books. They start off really simple, I reckon you could probably read the Level Start books even without knowing much grammar, though I already had a decent grammar basis when I found these so take that with a grain of salt.
For listening, you won’t need any kanji at all, just grammar and vocabulary. My recommendation would be videos like Comprehensible Japanese. Other people like podcasts like Nihongo con Teppei.
As for when to start, that depends. You could start today and struggle through deciphering sentences, or you could start once you’ve finished Genki 1 and struggle through deciphering sentences.