I want to jump in briefly and emphasize this. Here's a little peek (peak? π iykyk) at what that looks like in game. The system is pretty flexible so you can focus on content that you like to do!
Pretty much this.
Everyone gets the same number of objectives. This just determines what kind of objectives you get--this gives you some control over that so you can focus on doing objectives in game modes you enjoy. If you select multiple game modes, we try to give you an equal number from each one you selected.