as it was said above getting the II first has a higher pass rate for the initial and there are fewer things to do in the PTS to add on the airplane rating. i did the same thing. but the category and class rating thing applies. if you dont have the CFI-A (airplane) you cant set foot in a plane, when i got my original temporary it said on it "cannot act as instructor in an airplane"
by all means do the II first, but make sure you have a date for the CFI-A add on or you will legally not be aloud to do anything