Okay, so I'm new to eventing, I've made the switch after about 4 years doing hunters.

I took some straight dressage lessons and loved it, but missed jumping terribly and wanted to try eventing. My trainer decided to take me out on the xc course with her schoolmaster (rather than my green OTTB) and I fell in love! I have been practicing to event ever since. Unfortunately my horse had to be put down recently, but I am on the search for another OTTB. Obviously I won't be eventing in the near future, but I still have a few questions!
First, will I be penalized in any way for riding dressage in an AP saddle? I know it's legal to do so at low levels, but I'm curious as to if it will show on my score at all (assuming I don't totally mess up, obviously!). I know I'll have to buy one eventually, but I don't want to buy one just yet unless it's necessary. Unless someone has a money tree that is free to a good home.
Second, what's the most comfortable vs. cost effective approved vest for xc? Which one do you use?
Thanks guys!