I think Vitalik said around 100 million, but that was a while ago. I suppose we have to wait until PoS is in place first before we can get close to a definite answer. Total supply isn't the be-all-and-end-all though. I mean, fiat is uncapped so technically has potentially unlimited supply.
My thought that the fixed supply will have determined after the pos casper already implemented, that means about the next year we will see about the casper network will be alive.
The block reward will be decreasing a lot and just keep your ether.
Well that's good to keep our ether and if we hold it for so long it will eventually become expensive in value. I agree on the statement that the supply is fixed and no such unlimited supply due to it's been established same as with other currencies. If ever its supply becomes larger, I guess its not a good investment, because the value might not increase fast due to more supply and everybody can buy it in a lesser value. The appraisal value might not reach higher and will remain stable just like those shitcoins with billions of supply.