Re: "Crown-porcelain/ceramic substr" on a molar -
It's not a bad idea particularly.
The new all porcelain crowns are at least as strong as the old PFM (porcelain fused to metal) ones and are a bit more aesthetically pleasing. They also tend to wear the opposing teeth less since the PFM porcelain seems particularly abrasive.
Ultimately they aren't as strong as PFM so if you have a severe clenching/grinding habit then they wouldn't be suitable. Presumably you don't or it wouldn't have been considered as an option in the first place.
If the tooth has already been prepared for the crown, then it's too late to change things now, the three different crowns types have different ideal preps so they aren't easily interchangeable without a lot of messing about. I don't think that there's any advantage in changing it at this stage.
Despite appearances to the contrary, Gordon has been a qualified dentist for over thirty years.