Adopting before having biological kids

Hi, my husband and I are planning to adopt sometime in the future, and are not sure when exactly that will be. I'd like to adopt first (we've got some money, the time, the space, why not?!) However, we also don't have any biological kids yet, and my husband would like to have one or two biological kids before we adopt. We've been married for 2 and 1/2 years. I am 22 and he is almost 33. Our life is very uncomplicated right now, I just graduated from a university and we both hold jobs where we would be able to take off time to travel for the adoption, so I feel it would be the best time to go through such an arduous process as adoption (we're going to go with international adoption). Another aspect is that we've decided to adopt 2 kids, 4 years or younger. We've also decided to adopt HIV + kids. If we decide to adopt first we'll be getting an intense crash course in parenting! Yet another aspect is how the adopted children will react to any biological children we have in years to come. The adopted children will be the big sisters or brothers. Most families that I see adopting do so after they've had biological children, so the adopted kiddos are the youngest. Has anyone else adopted before having biological children? How did it turn out? How did the adopted children do being the older siblings to younger biological kids?