Tojiro IDK breadknife? (In da' kitchen?)
I don't think the breadknife is going to fit in that block, and if it does much of the knife will likely be sticking out. Your best bet for the ITK breadknife (which I absolutely love BTW) is a magnetic strip or a sheath for it.
The block should fit the santoku and 210, those are common sizes and I believe the Shun equivalents are taller meaning you should have some room.
As far as a carbon knife goes to compliment your others? I'd probably go with a 240 or 270mm Sujihiki.
Reason being: You have a 210 gyuto and paring knife. The only thing missing is a slicer, and you need something longer than 210 for your slicer in my opinion.
Since you would like to learn more about carbon maintenance and are going to be a home user, the Fujiwara carbon would be a good choice. It's cheap and tough, and will reward a user who puts a little time into taking care of it. Holds and takes a great edge, but steel is a bit reactive at first. http://www.chefknivestogo.com/fufkmsu27.html