Frieza is not the type of evil overlord who likes to eradicate life forms behind a desk, he's the guy who wants to watch the agony in a filthy monkey's eyes before he sucks the life from them, or to make them watch while he kills their family/species. No doubt thanks to countless years being far superior than anyone who could ever challenge him, Frieza had become comparable to a cat playing with a mouse. That said, when he goes up against an opponent, he knows they cannot beat him, and that they are determined to do anything to stop him with the same bravado as always.
He likely created all of these transformations so he could fight an opponent on equal grounds, build their confidence that they will "save their race" or "avenge their leader", blah blah blah, until he transforms into the next powerful level and drains all hope from the enemy before dropping them to their knees, thus it was not him "panicking" but just playing his little Frieza game.
This psyche control is super effective against someone like Vegeta, who can lose his temper at the slightest taunt against his pride. Without this control over Vegeta's emotions, Frieza surely would have fallen long before. Then he met Goku, the ape with the strength of a Saiyan, and the sense of humor of a human. He tried these games and after every power-up, Goku increased his strength to match. Because Goku didn't understand any of the politics or the crap around the empire of lord Frieza, he was immune to these taunts, and he has never been afraid, especially of a superior enemy. This is how Frieza's mind games played against himself and led to his own demise.
So to answer your questions:
It's very unlikely that Frieza was bluffing, but I don't have a scouter so I can't say for sure.
Yes, through intense training and his fusion with Neil, Piccolo was totally matched if not stronger than Frieza's current state.
Not afraid, but in fact, he decided that it was about time to crush the hopes of his enemy and put an end to it.
And the overall question
Why did Frieza need the second transformation?
Because it gets boring being the evil overlord of the universe, so he created downward, not upward, all the transformations to play with his prey before biting out its throat.