No, as the game stands right now you do not become an actual noble or get Knighted. (Not being knighted was a big disappointment for me, because I feel like stolen valor when people call me a Knight) I don’t know much about culture back then but progressing through the main story seems to give you a Nobles status. (without any spoilers
You can see at what levels you get perk points in the description of the skill. You can spend the points only in that particular tree. Remember you don't have to invest perk points right away, you can wait until the next point. The best example would be with strength's level 2 perks Gravedigger and Stronghold. In a nuttshell: Riposte (=Master Strike) is activated by just pressing the block key at the right timing (before the green shield appears) and it is performed automatically (no attack button needed) -> BUT: You need to unlock Master Strike via Training Master Strikes with Captain Bernard beforehand. ZPgEa.