Hi LizzieV:
 
First, thanks on behalf of your Pi for rescuing him.
 
If white capped Pis were dogs, they'd be those bark-y little terriers who are SURE they're bigger than a Great Dane.
 
For more information on living with Pis, look for the yahoo Pionus group (google it) & join - you will learn a lot. 
Pis all have different personalities, but my WC Pi loves apples & carrots & yes, they end up shredded. He once dove into my bourbon-on-the-rocks glass (I think he though I was drinking apple juice & not sharing). He surfaced pretty quickly, with a shocked expression.
 
Do NOT allow your Dad to share his scotch. Had I been fast enough, my guy would never have gotten his beak in the bourbon & he hasn't, ever since. 
 
I think changing homes is always temporarily traumatizing for birds - and they WILL pluck. Mist him with water every day or so.
 
They usually really enjoy it - I point the mister up in the air & the spray lands on him like rain - and he spreads his wings & dances with joy). 
 
Make sure they get a GOOD mix of seeds, veggies, fruits, greens & pellets. Keep giving them stuff they don't seem to eat - sometimes it takes a month or longer before they realize it really IS food.
 
I think he needs more attention that you were originally giving him & would appreciate more cage-cleaning (although I'm not terribly good on that score & know from experience they CAN survive in less-than-ideal cages).
 
Once he figures out YOU are his human, you will have a friend-for-life.
 
My Pi is sitting on my shoulder, cooing (squeaking?) quietly while I type. It is his way of telling me he's about to go to sleep. Once he squeaks his name softly, he'll be asleep for the night . . .
 
That's what you have to look forward to. Enjoy, relax, & join the Pionus group. 
 
But mostly, relax & enjoy.  Your bird doesn't know you never got the owner's manual.  He'll figure if it is okay with you, it is okay with him.