I pronounce it a-KAY-sha. For the plant, I'm pretty sure a-CASH-a is just wrong. But since it's a name ... I guess you could do it.
I never really went for the look of
Acacia. There's something about it that seems awkward to me, I guess the two different letters C so close together? And
Acacia has thorns. Big thorns. So I'm not into it. I think it's an okay name, but nms.
Maybe consider
Cassia (Cash-a) or Akasha? (See
Akash)