Is there a way to transfer WoTLK characters to a Cata realm?

I think there was a way to do it on Molten but I just never tried it.

Also on a scale of 1 to 10, how buggy is Cata?

You can't transfer ur characters between expansions.
And I can't say how bug-free is Cata as I haven't played since the FL HC release.

sadly you can't transfer characters from WOTLK->Cata although i wouldn't recommend going to cata as it is very very buggy.