Shall we ask if a sorcerer can learn the same spell more than once? Can he learn less than the 4 cantrips and 2 1st level spells at 1st level?
No on both. It's the same for the crusader.
However, there is one little thing on page 47:
Much like a sorcerer’s spells, each stance or maneuver is a specific ability that a character might know.
Each one is a unique ability to either know or you don't. You can't take it more than once.
As for a rules quote on whether you can take less maneuvers or spells than you're allowed at a certain level, it's very doubtful you'll find one because it's one of those things the game assumes you'll do. It's as "duh" as saying a human has two arms and two legs.