I would say try and speak as much as you can! Even if it's just to yourself, every bit of practice helps! For example, when you wake up in the morning you can say to yourself, "I'm going to eat breakfast now" in Japanese「今、朝ご飯食べます」As for listening practice, I would say watching Japanese dramas or anime is a great way to pick up new words and to get use to listening in Japanese. Don't worry too much about not understanding everything, just getting use to how the language is spoken is good enough (be aware though that some of the language in those shows can be rude in real life).  For practical purposes, typing in Japanese is a more effective use of your time than writing the kanji on paper because most people nowadays type instead of write, but that's just my opinion. After you finish Genki II, you should be upper beginner at that point and should be ready to switch to an intermediate book like Tobira, for example, but there are many others. As for your last question, I personally think learning kanji should start from the very beginning going side by side with your studies of grammar, I just think it makes things easier that way. I'm still a beginner, so most of the advice I'm giving you is from word of mouth from my more advanced friends and my tutors here on italki, so take it with a grain of salt. 頑張ってください！

I would say as many hours as you can stomach before your brain turns to mush. :P If you mean actually talking to another human though, I recently tried something new that I quite like. I have another Japanese learner who I meet with once or twice a week and we decide on a grammar point or topic ahead of time, and we promise to stick in Japanese only. It takes away the anxiety, and gets us in the habit of communicating in only Japanese. I've not been studying long, but I find that we stick in Japanese for upwards of an hour each time and I have loads of fun coming up with funny sentences and seeing what he comes up with as well. :)