How and when to use anki decks?

I had a similar issue when I tried the core decks. You could try torii, it goes through the core 10k, but you have the option to set it to show the words in order of kanji learned in wanikani. Therefore, you will only be seeing words with kanji you learn. It’s not based on frequency this way, so you may see relatively infrequently used words, but you won’t see anything with kanji you don’t yet know.

Or you could go the manual route, which I started doing before I discovered Torii (and I’m too far in to give up on it now). I wouldn’t necessarily recommend this, since it’s a lot of work, but it ensures you only learn words with kanji you know. For each kanji you know in wanikani, look up all the words using that kanji on jisho. Anything with a tag of JLPT3, JLPT4, or JLPT5, add to your deck. Since this is also a massive time sink and arguably a waste of time, I only do this while passive listening.

Another option is to pick up a kana only deck and start working on that first, then when you have more kanji experience, go back to the 2k deck.

You could also go into the 2k deck and suspend all cards with kanji you don’t know. As you learn more kanji, un-suspend the words. Actually, this is probably the best course of action.

Regardless, I personally don’t recommend waiting to learn extra vocab if you’re able to handle it alongside wanikani, even if it’s just kana words. Even if you only learn 1 word a day (which is what I do when I’m getting overwhelmed), it’s better than nothing, and you’ll be that much more ahead by the time you start consuming native material.