Are these finches compatible?

I currently have a male shaf-tailed finch and a female zebra finch. I am planning to get another female zebra finch and something else to keep the shaf-tailed company. I am interested in a cordon bleu but do not know if the zebras would be compatible with it. They have a very large cage (around 38"x38" base and 5ft high) Would the cordon bleu be ok or would I be better off getting another shaf-tailed (much harder for me to find) and what gender would be best to get?