Rolling resistance is also a huge factor in tire choice. Probably a bigger one than aero.

As far as "breaking in" goes. I just make sure I've got two or three rides on a new set of race tires before I race on them. After that, I just save that set for race day.

When tires start looking a bit square I'll retire them from being race tires. How long that takes varies widely depending on the kind of racing you're doing and the tires involved. For training I ride tires until they physically start falling apart.

Choosing a good tire (and tubes) is an important decisions that is worth some research. Worrying about breaking them in and when exactly to retire them... less so.

Thanks. I am running Conti GP4000S with latex tubes and a little Stans in them. I'm just trying to figure it all out.

You're on the right track.

As far as the "stacks" of old racing tires...most people would just start using them for training when they're demoted from race status.

Can't go wrong with Conti's. Carl Spackler got me going with 25 mm. All season's for training; 4000s for racing. If they're good enough for him, they're good enough for me. So far, I love them.
Marty