The Battle of Yavin (according to SW Wikia) involved 30 Rebel starfighters. All but 3 were destroyed.

I counted roughly 25 pilots (plus Luke Skywalker)in the briefing room.

The medal ceremony featured at least 45 pilots celebrating.

Does that mean that the Rebellion had around 70 pilots for the Battle of Yavin but only used less than half?
Did they all not have ships?
If there were limited number of ships, why did they let a moisture farmer who no one had seen fly a ship up until that point take one of the precious few starships they had?
If they had plenty of ships, why did they send the guy who just walked in the door with no previous experience on the most important mission of their young rebellion’s existence?

Is there an official explanation as to why Red and Gold Squadron were essentially wiped out but there were probably one or two more squadrons at the Yavin ceremony that went unused?