Why don't you get some coordinating yardage in a light color. Moda has some great blenders, or any line. That way you have more fabric to play with. I also would start with a pattern. You sound just like me, and I can drive myself crazy trying to figure something out. Patterns make it so much easier. A dnp sounds like a great idea. (and no sea scapes won't be too busy, it's gorgeous) Use a small print in the middle, because that square will be cut up the most. Then the yardage can fill in where the charm pack repeats or use for borders. You can't do a whole lot with just one charm pack. It can take at least 2 to get enough for a quilt bigger than a baby size.
Also, go to YouTube and watch Jenny from Missouri Star. She has a lot of good advice for beginners and a bunch of tutes on quilts to make with precuts.
I taught myself also, and I have learned a lot here, and from YouTube and from good quilting books. Good luck and please show us a picture of what you come up with.