Thank you both. I just tried the 3D stroke trial and while I haven’t come to term with what it can potentially be used for I have used it in it’s most basic form to achieve what I described in the OP (the mask) which made it quite easy, and with surprisingly good results, it’s not half as cheap looking as I expected, probably because the animation is quite fast.
However, when I export I get this horrible X over the swirl:

I assume this is because I am using a trial, but just maybe this is something I am doing wrong? If so, that growing tutorial looks great, thanks.