Hi there. I think the design is cool and it has the meaning that this plant is rough outside and soft and juicy inside. But it's just my opinion, don't take personally))
Btw, i didn't think of tattooing a cactus. I see it's a good idea, but I would do it like in 3D you know? I love 3D tats...
About the place on the body, I'd recommend chest. Don't know, I think it'll look awesome there....