To understand Torah, the Chafetz Chaim is helpful, but to my understanding it would make sense to get the Avi Ezri of Rav Shach. The reason is this. Knowing Hebrew is in fact some help to understanding Torah, but not as much as you might think. 

What you need because of limited time is something small and simple that gives you the basic idea. That is definitely Rav Shach's book the Avi Ezri. What he does is to give a good idea on how to analyze any given halacha in the Torah in a very deep way, but also in a very simple way. 

I could recommend Rav Chaim HaLevi Soloveitchik's book the Chidushei HaRambam, but there is something about Rav Shach's book that goes way beyond the Chidushei HaRambam. But since the Chidushei Harambam is smaller you might try to get that and to work on just one long essay.   If you have the Chafetz Chaim in Hebrew his own notes at the bottom of the page are also excellent ways of learning how to learn.

I cant really explain very well what the thing is bout Rav Shach's book. It is simultaneously simple to understand and yet very deep. However I admit that it was Rav Chaim Soloveitchik who opened the door to the Rambam.  There were some preliminary steps before him but they were just cracks in the door. Reb Chaim opened it swung it open. Rav Shach then walked in. That being said if possible the best thing would be to get the books of his two disciples Barch Ber and Shimon Shkop and just plow through them.