How do I prepare for the MCAT and Medical School?

If you find a post-degree program, make sure its specific to pre-medicine. Nursing won't cover all the bases, especially LPN-level. You need A year of General Chem, a year of Organic Chem, a year of General Bio, a year of University Physics, and Calculus. Some schools do have additional requirements so be sure to check ones you're most interested in. I can't help you much with the MCAT. I really don't think a second degree is warranted, unless you'd want it anyway.