Whenever you feel ready. There’s no automatic progression in renshuu that spoon-feeds you material in a certain order. To start learning kanji, you need to create a schedule for kanji. The easiest way to do that is to use the Manage your schedules link on the dashboard.
Also, I recommend reading the section of the help titled I'm a beginner. What should I study first? Click on (?) in the menubar, then Top Questions, then scroll down.
Finally, welcome to renshuu. I hope you find the time you spend here rewarding.
As someone who started early (directly after katakana)with the kanji I can highly recommend it. I started with just the meaning and no kun- or onyomi. The readings you can pick up later when you’ve been exposed to more vocab with those kanji. Just start with the n5 list and anywhere between 1 and 20 kanji per day depending on how much time you have. I aim for 80-90% correct, if I fall below this I slow down and above that I go a bit faster.
