No problem...it's Monday morning...and I don't mind repeating myself, especially after I've led you around in circles. And I will do it again... Now.
Please remember one of my guiding principles: "Don't optimize until you need to." I repeat this one because I think it makes sense. Basically, it's a specific instance of the "just in time" principle. You've chosen to optimize your fact table by aggregating (because of the expectation of excessive size, which I understand) and I've convinced you to optimize your external number dimension by creating a sub-dimension (again because of the expectation of excessive size). Given those, I wouldn't worry about any further optimization in your application until it's shown that you need to. Optimizations take time to plan and execute so you shouldn't let them stall your project and delay the delivery of some very useful analytics.
Java 1.7 (64 bit)
MySQL 5.6 (64 bit)
Windows 7 (64 bit)