Awesome!
So my overall study advice is that in general, doing a little of different areas of the language (reading, listening, speaking) every day is going to take you quite far. Probably farther than just doing a bunch of grammar study and nothing else. So I would recommend a balanced approach where you start to mix in reading and listening to materials made for learners (and then native material when that gets too easy) with grammar study.
Output
You mentioned having iTalki sessions for conversation, so seems like you have output covered.
Reading
At this point (almost done with Genki 2) I would recommend starting to read if you haven’t already. Satori Reader is an excellent resource and what I’d recommend first, and there’s a Satori Reader appreciation thread with a lot of peoples’ thoughts on it/reviews if you want to check that out.
Listening:
Adding a beginner podcast for 5-10 minutes a day into the mix would be good if you haven’t done that already. Here’s a Master List of Japanese Learning Podcasts to get you started there too! If you have a commute or chores where you can fit this in, that’s the best way. Don’t sweat not understanding everything at first.
As for the content of the textbook…
Kanji:
How much kanji have you studied? In Quartet, they begin to remove furigana on some kanji, but your level 4 on Wanikani would be a bit low for the difficulty of the Quartet kanji. So you’ll need to decide how you want to approach kanji- if you want to commit to WK, or if you want to use a different resource.
Personally, I did all my kanji study on WK and ignored the kanji sections of Genki and Quartet entirely. So if you have a resource you like better, you can ignore those sections of the textbook. I think @mitrac uses the Kodansha Kanji Learner’s Course which is another option.
Study Schedule:
Here’s what I do:
- Watch Tokini Andy’s Quartet videos at a pace of 1 grammar point per day (10-15mins per day)
- Now that the grammar has touched my brain once, read the grammar pages of Quartet. These are quite long, so I recommend splitting this session up. You could do 1 or 2 points per day if you want to go very slowly.
- Now that I understand the grammar covered in the chapter, I do the two required readings, as well as answering the before and after reading questions. I like to listen to them while reading along first, then read again with the vocabulary booklet in hand to check definitions. This could also be split up into two different days.
- Do the listening sections, these are pretty short
- This is where I would do the essays, but, full disclosure, I gave up on doing the essays and started skipping them
These are a lot of work and if you do them I would advise budgeting plenty of time and doing them a little at a time instead of in one long session.
So a daily schedule, assuming you have an hour a day for Japanese, might be something like:
5-10mins podcast
15-30 minutes reading
15 minutes Quartet study
Then weekly, your italki sessions. This can of course be edited to your needs, but at this stage it’s a good idea to start dipping into other areas of the language (like reading and listening) and not just relying on textbook study! Of course, if you’ve already started doing that you can go ahead and ignore everything I just said
Finally, welcome to the forums! 
Feel free to keep looking around, there’s a lot of great advice and community support here.