Is it obligatory for the neck bones to be level and for one to look straight ahead when rising from bowing (rukūʿ) and standing upright?

Moderation after bowing (ruku') is a pillar (rukn). It is recommended that the neck be straight, but a slight curvature does not negate moderation and is not harmful. In fact, it may be necessitated by looking at the place of prostration (sujud), which is an act whose recommendation has been mentioned in the Sunnah and is the view of most scholars.