What are the benefits and drawbacks of doulas?

A good Doula. Can be erty helpful. One drawback is looking down upon epidurals and having women feel bad if they need one for pain control. Remember, they earn a living by helping people through pain, thus they are biased toward not getting pain relief. If oriented that way, go with a doula, you will need all the help you can get. Good luck, congratulations.
Benefits only. I think doulas are great as long as they don't marginalize your partner or husband. Anything or anyone that increases your chances of an easy, healthy vaginal delivery is great.