If you are storing your bitcoins on a wallet with private keys then you can use those private keys to access your wallet even without the password. But if you created a wallet but you do not have the private key because you created your wallet on a website that hosts a bitcoin wallet then all you need to do is to contact their support.
Yes, but you will need to prove that this is your wallet.
It may be very difficult to recover your lost password but I wish you luck.
Try to find first email you received from them.
Yes，and if you lost your privatekey, there is no way to recover it，if you have your wallet.dat and lost your password, maybe if you put a weak password, you can bruteforce it.