How much D-Phenylalanine (DPA) would you recommend that I take per day?

I would start with just 500 mg per day and see how you feel at that dosage. The most I have ever taken or recommended was 500 mg, three times per day. But I would just start with 500 mg per day.  

But you might not need to take it every day. I found that the benefits would last for a few days. So I started taking it every day, but then eventually I was taking it just 2 or 3 times per week. Then I was only taking it once a week. And now I don’t take it at all. I was able to stop it over time because I did EMDR and neurofeedback.