OK to upgrade my LTM from 11.6 to 12.0?
I'm waiting for 12.1, just to be sure.
You shouldn't have issues upgrading from 11.6 to 12.0 but as always I would make a UCS backup and read the release notes before.
It depends on you... If you feel comfortable to upgrade after going through the release notes.
Make sure that you take 12.0 HF1 as well. I have been very happy with the stability of 12.0 so far.