Do you recommend that we start our day at Studios and end our day at IOA?

It can work either way, but starting at Islands of Adventure may end up working better. First thing in the morning and in the evening are the two times of day with the lowest waits. Either way you'll be at one park during each of those times, but if you start at the Studios with Early Park Admission the waits at a few of the attractions -- Gringott's, Mummy, and Despicable Me -- will already be a little higher than they would be without it. As I said, it's perfectly doable because there will be low waits for other attractions that weren't open during the Early hour, but you will have to wait a little longer for those.

I would suggest testing using some different plans. Start one in the morning in each park and then another with a start time around 15-30 minutes after the first ends and see what works out better.