Some will state that pattern is free for personal and school use. Some restrict it even further by only allowing downloads without distribution. When in doubt, leave it alone. You may not be able to use it, but often it can inspire you enough to create your own patterns. Whatever you're most comfortable with.
Acrylics dry quickly.
They are water-based. They're accessible, no need to visit a specialty store or craft outlet. They come in every color you need and when you can't find a color, you can mix it yourself. By all means, do so especially if you are doing this project with your kids. It's a lot easier.