The biggest value of coaches is their outside perspective. Many coaches who still actively train themselves still retain their own coach. Why? Because we are not objective about ourselves. It is much easier for a third person to see whether you are heading towards a cliff, because you are doing too much. Coaches are helpful focussing your attention when needed. They can help you decide how much intensity and volume you should do, and what you should work on for a given season.
I don’t think the biggest value of coaches lies in the selection of individual workouts. Of course, they will do that, but in all likelihood they will adapt your training plan less often than TR (I’m assuming you communicate with them on a weekly basis).
That depends on who you are. Really ambitious people have multi-year training plans. That doesn’t mean that they know what to work in 3 years from now in the 16th week on a Tuesday. But that you have decided on what the overarching goals are.
TR’s Plan Builder will disclose a whole season’s worth of workouts, but with the understanding that most of them will be substituted dynamically. Your training plan can get updated after every workout or training plan deviation (e. g. because you are sick).