I would have picked two of the same healers and tanks, or made more symmetry between the groups. The DPS are still good to be mixed up if you just make castsequence macros and group similar abilities onto the same buttons, but the tanks and healers should be more in control than what you will end up doing with them as mixed classes. I guess you should practice a lot in Kara and ZA before you do Naxx to see if you can work it out.

My solution to 10 man boxing was to have 2 computers 5 boxing, and each main window was a tank wth its own mouse. Then I push a button to focus one or the other tank, or to split focus, and attack the focus target. And both of my teams are almost the same, so that by doing 5 mans with them I get really good at knowing what they're doing, and then doing 10 mans feels really natural. I tank and heal with different buttons than I DPS with, also. I think you ought to consider that. Try to avoid castrandom macros, as well. Plan it out, don't let the game decide for you.