Yes, you can mix them up to see how it all goes together. Some people test them on Q-tips first by dipping one end in each fragrance to get the mixture, Not sure how that would work with 3 different FOs though.
I am not sure about the answer for the DPG question though. My thoughts are you need to add something to the FO to dilute it a little or the FO would not burn so well on its own. Might be a good Google question.