It all actually depends on the speed of your work and how much you progress. I wouldn't recommend rushing in 4 months as taking time to learn and really understand every part of the two books is essential. But if you are sure that you are a fast learner, then go ahead! Maybe instead of thinking about how many hours, but how many chapters you can complete... Maybe 2 or 3 a day? It can speed things up. But i would say about 2 hours should be spent on that. And practicing pronunciation with the CD and stuff.. and finding someone to talk to regularly can help

One or two hours a day. Spend time each day first working on practicing what you learnt the previous day and then move onto the new stuff. Repeat. It's helpful to post notes here or on lang 8. You can find language partners. I think Genki can help with reading and writing and possibly listening but you really need to find someone for speaking practice. :)

You could certainly try there are a lot of exercises and a lot to learn. It's good to practice it too. I think it would be quite intense but it's not impossible. Just pay attention to how much practice you give each section.