The Holiday's have enough emotional baggage without the added stuff of coming out. That said, waiting until things are 'calm' could be like waiting for forever. Sometimes we do have to seize the moment. It's a dance that one can plan for, but often must improvise to suit the moment.
Writing letters is a good idea.
I gave my parents a list of books to read, but to this day don't know (and doubt) that they read anything on it. Parents can surprise us though. Your father is a pastor, right? He's probably going to swing into preacher mode at some point, and your 'dad' isn't going to be in the room. Can you reach that person? Good question. You parents are going to need time to deal with the news, even if they 'know' it on some level. Give them time by not inundating them with information. They will let you know if they are receptive of not.
One thing is for sure: you won't be the same person after you come out. That is, you will be free. A very good thing.
Hoping that it goes well.
Oh. Make sure you have a support system when you decide to take the step. You are going to need your friends. Big time. So get that in place, OK?
Be the love you seek.