The prone condition does not list any limitations on movement other than that standing up from prone is a move action that provokes an attack of opportunity. So...
1) Is movement while prone considered crawling?
2) What movement is required to move from prone to sitting/kneeling (roughly half the penalties of prone)?
3) Does a prone person get a 5-foot step (if 1 is no, then why not)?
Pg. 568
Prone: The character is lying on the ground. A prone
attacker has a –4 penalty on melee attack rolls and cannot
use a ranged weapon (except for a crossbow). A prone
defender gains a +4 bonus to Armor Class against ranged
attacks, but takes a –4 penalty to AC against melee attacks.
Standing up is a move-equivalent action that provokes
an attack of opportunity.
Pg. 186
Crawling: You can crawl 5 feet as a move action.
Crawling incurs attacks of opportunity from any attackers
who threaten you at any point of your crawl. A crawling
character is considered prone and must take a move action
to stand up, provoking an attack of opportunity.