Bunpro as a supplement to WaniKani

Wanikani is for Kanji learning. Bunpro is for grammar. I don’t see how they are going to clash. You might decide to spend more time on one than thw other, aside from that there should be no cause for concern.

You can pick it up whenever, however Koichi recommends starting grammar from level 10 wanikani so I guess you can wait until then?
Personally I’m trying to fit bunpro into my schedule while doing Genki.
Genki is a nice grammar textbook if you want to look into that.

Here is a list of resources you might want to check out