If you wanted it to be balanced with the first way (Apprentice & Shoto) you'd probably want the longer blade on the shorter hilt.
Personally, I would get two exact matching hilts with the same length blades.
You would probably want two Shotos with 26" blades at your height. Possibly 30" thin-wall blades from another vendor (SF only sells thick-wall) to reduce the weight and make it easier to spin. 18" blades are super short and really just meant for children imo. I would recommend the Sentinel/Arbiter or Bastion Shotos.
One thing to consider with Shoto vs. Apprentice is the size of the grip area that they would give when paired up. The Bastion Shoto is 8.25", so two of them paired would give you about a 16.5" grip area (Bastion is the smallest Shoto). The Apprentice Bastion is 10.8", which would come to about 21" when paired up assuming you use the "Staff Coupler Short". Using the "Very Short" will actually make them somewhat shorter, since you lose the length from the pommels... and the "Long" one will add about an inch on average. Do note that the Acolyte/Disciple can only use the "Staff Coupler Long" due to pommel design.
Most Shoto hilts are about 1.5" shorter than their Apprentice version, so you'll average about 3" longer on the Apprentice staff vs the Shoto staff, depending which hilts you were actually thinking of using.
Another thing to consider is that the Shoto hilts have shallower blade sockets than the Apprentice hilts. The Apprentice Oracle in very shallow to begin with, and it's much more pronounced on the Shoto. Deeper blade sockets help keep your blades in better.