Hello!
I'm not sure studying vocabulary by itself is the best use of your time. Clearly, having a better vocabulary would be useful but I think the best thing for you to do is to practice reading and then look up all the words that you don't know. If you were going to take the GRE I would say that learning vocab by itself would definitely be worth your time but since the GMAT doesn't directly test vocabulary and does require a good reading level you would do well to work on your reading ( I usually suggest doing an hour a day if you can). Start off by using the op-ed section in the new york times, and then as the test gets closer start doing some of the reading passages in the official guide.

Those are both good choices

I agree that it's a good idea to read business papers but make sure you don't concentrate on them too much because the GMAT has reading passages that come from many different subject areas.