Veldan, I can't give advice as to being an adoptive parent, but as an adopted kid I will give you a few words of wisdom that helped me when I was growing up. My parents were wonderful about a lot of things but these were the main ones:
1.) Never, ever lie about him being adopted, even if you get a younger child that doesn't remember his birth parents. My parents were open and honest about it from the time I was old enough to understand the "dumbed down" explanation of what adopted meant! Trust me when I say...he will appreciate that honesty!
2.) Always be honest about how much or little you know about the birth parent(s)! If the parent(s) just flat out couldn't afford to feed/clothe him, let him know that, along with the fact they loved him enough to give him to someone who could! You don't have to go into detail, but if he was physically abused, don't try to hide it. If he was sexually abused, don't hide it but don't get into great detail.
3.) MOST IMPORTANT!! Let him know, in words and actions, how much you love him and love having him in your lives! Let him know that you will support him (not necessarily financially but emotionally) in whatever he wants to achieve in life! If he was given up due to circumstances that will allow you, in good conscience, to help him track down his birth parents when he gets older...DO IT!!
My parents were (Mommymunchkin still is) the greatest parents in the world! Of course that's my opinion, but still! They did all of those things I just mentioned! Yes, my circumstances were different than you adopting an older child, since I was adopted at birth due to Max having 9 kids already and not being able to afford to feed/clothe me, but still! The best thing they did was be COMPLETELY honest from the time I was old enough to understand. They supported me, emotionally, in my search for Max. They supported me emotionally when I went to meet her! My Dad went with me to my birth Father's funeral! Mommymunchkin sends Max flowers on her birthday and on Mother's Day! They didn't have to do those things...they could have just said they didn't know shit about my birth parents and told me to STFU, but they understood that wouldn't be a good thing in the long run. They were honest, understanding, but above all, they were loving, even when I wasn't very lovable!
Looking back on it now...there were a lot of times I wasn't very lovable. It is hard being an adopted child. It takes patience and a lot of love to be the parent of an adopted child. It's a very psychologically difficult thing, being that child. I am sure it will be harder being an older child who remembers his/her birth parent(s). No matter how much love is in the adoptive family, there is always that question, "Why did my birth parents not love me?" in the back of the kid's mind. Since you want an older child, the suggestion about a psychologist wasn't a bad idea at all.
Having had that little rant! Now I will say...best of luck in your endeavor! You (don't know your partner) will make a wonderful Daddy! Just remember...love and patience is the key!