Hello,
There are a lot of questions here. I will do my best to answer all of them.

I am sorry you lost access to your email account. Fortunately, you do not actually need it to play the game. With your previously-gmail account bound as an oasis account, you can log in without accessing gmail at all.

Unfortunately, no, you cannot change your registered email. You can, however, change your security email in your user settings.

Lost items will require you to put in a CS ticket. Here is the link:

https://support-center.oasgames.com/

Thanks and have a great day!