I think 30weeks sounds just perfect. I started mine at 32 weeks and i really enjoyed it. Yes, i got a bit over the waiting for bub to arrive but it was so nice to be able to relax and enjoy those last few weeks of being pregnant. I had to take it easy due to PE but i watched loads of trashy tv and had a few friends on mat leave too whom i caught up with.
Do what feels right for you but i personally think that starting at 30 weeks if you can is a great idea.