Gutterman's thread is very popular here. It is polyester and will not rot or degrade in sunlight. Nylon thread is not the way to go for outdoor projects. The thin and slippery materials such as silnylon are difficult to sew so I would not start with them. Many projects on this site start out with 1.9 oz. ripstop which is not too hard to sew. Good luck and have fun and remember there is a learning curve so don't get frustrated.
When it goes over their heads, it really doesn't matter how high it is.