Welcome aboard and congratulations on your GT/CS, gotta love the California Special!
7% oil life, means when you get at 0% you just need to change the oil within the next 100 miles. So yes, you can drive with no fear even if you have 2% oil life left. Kind of weird the dealership didn't reset that when they sold you that Mustang, I would make sure with them that they did the oil change.
From now on, you should see this sign every 10,000 miles (more or less depending on your driving).
As for your lag, with your automatic, I've heard that before too (I have a manual), and I think the only 2 options you have is getting higher gears (3.73s should do), and/or a tune; that will do it (I've got the Ford Racing Tune, but I've heard it's not that great with an automatic, so you might want to consider another brand like Bama...)