From my own personal experience, you should aim for enough seal scrolls so that you can hit the top tier rebate. For example, the previous Seal Recruitment rebate allowed you to use 300 scrolls and a rebate of 66 seal scrolls. However, since that recruitment rebate gave out permanent seal scrolls, you only technically needed 264 scrolls because hitting the 200 seal scroll rebate gave a total of 36 scrolls. 264 +36 = 300 seal scrolls, which hits the next milestone.

Hope that helps!

~Jib