I am waiting until this sunday (day 9) before I open the hive up. I started this hive with a 7 medium frame nuc from NJ - put into 2 mediums, 4 frame in the lower box, 3 in the upper - going foundation-less.
My opinion that it's a bit premature to add an extra box at this point. Am I understanding you correctly that you split up the 7 frames into two boxes? If so, that sounds bit unconventional and would be something new to my ears.

The following are questions that I have at this point:
- Do you look for the queen specifically or just for existence of a queen (i.e. laying patterns)
- Are there any tricks to locating the queen? Being a new bk, I am not too confident in my abilities
- Is a good rule of thumb to add a new brood box (a medium) when I only have 2.5 frames or less empty?
At a minimum, your first fun task is to look for eggs being laid which will indicate a queen. It won't be required to find her and this is a learned skill that takes some time and patience. Give it a year or so and you'll start to find her fairly quickly, depending on how much time you spend checking hives.