I highly recommend a sulfur free plasticine instead of clay.
Clay is water based and will dry out and crack over time unless properly sealed. (I'm also assuming your talking about the kind of clay that come from the ground)
Plasticine is oil based so it not going to dry out, so you can leave it out for days with out worry,
I'm interested in what you are planing on sculpting
maybe able to give you a better staring point