It's possible that some people adopted from overseas don't have issues and some adopted domestically don't have issues either, but I do think 'issues' (sorry I can't think of a better word) related to adoption are very real for many children and adults.
Children adopted from some countries do not have any real knowledge of who their birth parents are or anything to do with their extended birth family. It may be a shameful secret in their country to have a child if not married and therefore even the relinquishing of the child was done in secret.
There used to be a list of videos somewhere on here all about adoption related documentaries etc and some of them are excellent in providing additional understanding.
I don't think domestically adopted children are more prone to trauma but I think it is better understood and if you adopt domestically you may find out a lot more about your new child's medical and family history.
Our son was adopted domestically and we know limited history. I still sit in the doctor's surgery and they say 'Does XYZ run in your family?" I used to explain to the doctor my son was adopted and I didn't know. But he was so upset one time by my explaining that, that I stopped. I now say "Not that I know of."
I guess what I am trying to say is that sometimes ignorance isn't bliss and sometimes knowledge is power. Knowing more about your child can help you to parent better and look out for them.
Overseas adoption is a wonderful thing but it is costly, it can take a long time, (longer sometimes than domestic adoption) and you may find you have issues you were not expecting.
I also think you are over thinking the birth parent contact. Most people I know who have adopted (in England) don't have face to face contact with any birth family members. If they do, it is usually siblings or grandparents.
The letterbox contact is simply a letter sent, usually annually, from the adopter to the birth parents, and sometimes, replied to by the birth parents to the adoptive parents (this is my experience, it is not to the child, not in our case).
The child you adopt is completely your child, legally and emotionally. They do, however, have another birth family and that is always going to be the way.
I was very keen on overseas adoption many years ago, the high cost, my age and the long wait put me off adopting from China. I do admire anyone who does it, honestly. But I don't think it is necessarily any easier. However, I really do not know how things work in the states so you may have had experience of this that I do not know of.
Good luck whatever you do decide to.