You can take as many bags as you like if you are willing to pay the excess.
If you want to know the included allowance I would look here
https://www.thaiairways.com/en/travel_information/baggage.page
It seems to me that your allowance depends on the fare type as is fairly standard but you can...
I did PY on JL MEL-NRT-LHR once. It was ok I guess. As you say better than Y but not J by a long way. I'd certainly reposition for J if the option existed.
I agree, if you don't buy at full RRP you are definitely missing out on the better wines of the world.
Most good wines don't get discounted unless they are mass produced (Penfolds etc)
Should reinforce that I cancelled 30 days after my annual fee posted with the guarantee that it would be refunded in full as I hadn't used the current years travel credit. I don't think that any other credit card provider offers this.