User blog comment:Solara184/Hmmmm should I or shouldn’t I?/@comment-38439752-20200304170506

Math side: it's possible to own pairs of all common horses without running out of room. Even more so if you only keep pairs of the t4s you have and for those that you don't have the certificate yet, one t3 while you wait is enough. After all, once a t4 certificate is available, most have their t4s outside, so it's easy to find a breeding partner for your t3.

When you upgrade all of your GS to the max level, you have 65 spaces each in UK, US and Germany, 50 in France and 48 on Fantasy Island (so a total of 293 GS spaces). Currently we have 72 common horses, so as pairs that would make 144 horses to keep. They fit very nicely in less than three countries, leaving you a one whole ranch for all the Exclusives you get and another for any other purpose you want (eg. mustang breeding). They take less than half of the total GS space, so you have plenty of space for the Exclusives, the odd fantasy horse you may get/keep, and the Constellations you already have.

Opinion side: I'm a collector, so I always recommend getting all t4s you can, since you might regret later on that you skipped something. The space is not an issue (yet), but if it ever becomes one, that's when you can start thinking of only keeping eg. one t3/t4 of Elite/Mythic rarity, and only pairs of the Legendary t4s.