They are separate rods and balls. Our set has some smaller rods, some larger ones. My son played with them a lot when he was two. You can easily make squares. Obviously the bigger the "building" the more support you need, but small things don't need much support, if any.
As to the magnets, they are decently strong - we've played with other brands of magnetic toys like this and these are by far the strongest. But a large creation wouldn't hold up to much transport unless you were very, very careful. But this morning my son built a snake with 3 or 4 rods as the body and a pyramid shaped head with balls and rods, and he carried it around by the tail for awhile. It only fell apart when he shook it. Hope that helps?