I think 总之 is "in summary" while 卒之/足知 means "finally".Yes. 总之 and 总而言之 literally means "in summary", and can be used in the sense of "anyways, in all cases".
But still, I cannot see difference between 卒之 and 总之.
It seems your 足知等到九月啦！can also be 总之等到九月啦！
Can someone explain?