Hi Buff and congrats on taking the plunge!!
I would study until you feel comfy. In fact you might want to overstudy since one, like you said, if you don't do well you'll feel discouraged to go on, and two, A & P is a toughy (sorry but it has that reputation --- which I happen to agree with having taken it myself). Once you have a couple of tests under your belt you'll know what study method works for you.
As far as having an old text, I used my A & P text from when I was in school 10 years ago and it did the job. Don't worry about buying the EXACT text that they recommend. Generally, A&P is A&P, med surg is med surg, etc.
Best of luck!!