We're new too so I don't have much advice to offer. I will tell you that we have 2 birth children and originally thought we'd take 1 foster child. A sibling group (twins) came into care and we accepted them. It has been a month. THey are tough to handle as well. Many tantrums and lots of screaming. My husband is very involved with them as well. A real hands on dad. (Thank goodness) It takes both of us to keep up with the four kids. Plus, our birth kids (ages 8 and 7) are awesome. Things are getting easier. Or maybe we are just getting used to the chaos.
I guess I would consider how much support you have from family, how much time you'll have to offer another child, how much patience you have left. Basically can you meet the needs of another child and still continue meeting the needs of the rest of your family?