excuse me for my stupid question but when will all ether be mined? Will there be a need for gas than? Also, is there a max supply of ether?
As there is no max supply to Ether, answer is simple : ethers will never be completely mined.
However, for your information, the way of mining ether is going to change in the next forks as Ethereum Blockchain will move from Proof-of-Work to Proof-of-Stake .
You'll finde more information Here