Overall GMAT FE help

Hi. 12 hrs/ week is great. It can be tricky to study in college and then also study for the GMAT, but if you can put in quality time (early in the morning type of thing, that would be great).

As a college student, you should usually be beating us old folks in terms of your freshness with high school math and things like that (though there is no more grammar).
On GMAT Focus, all your scores and sections add up to the overall score equally (not the questions you got right but the scores on a section), so it makes sense to max out your sections based on what you love and can do well. So i would start with your best performing section - something that you enjoy the most and can hammer the most.

In terms of course/books vs. questions and poking around GMAT Club. Both methods have been used and both work for certain situations.
Using a methodical approach with books or a course covers everything - that's like using a big paint roller and covering large areas of wall space - works great if you are starting out as it gives you a plan and focus. It tends to be more efficient as you cover material and don't have to go back to it. Using the question approach, you are touching up things here and there with a brush, and it works if most of your wall is painted but it is a slug if you are painting a wall with a small touch-up brush. There is also no end in sight as you keep solving questions sometimes for months.

I would say that you don't want to take up the methodical approach until you have the time. Ideally you study for the GMAT only for 3 months and mo more to avoid memory leakage, so get a calendar out, mark the best 3 months and then plunge yourself into it. The key is staying committed and focused. What you use is almost secondary.