The trailers don't need to be watched. They are events that take place before Volume 1 but they are not in any way essential viewing.
But I do agree about World of Remnant, they should be watched with the episodes, in the order they were released. Again, not absolutely essential but they explain things as they become relevant. Since there are entire videos made to explain these things, there isn't much of an explanation about some things in the actual episodes, if any at all. So without watching them, you might be a little confused or just unaware of a few things.