could I change the from address of email send from virtualmin ?

Virtualmin
1

A email will send to the virtual server’s owner email address for every new created virtual server.

However the from address is something like webmin@hostname.mydomain.com.

Could I changed the webmin@xxxxx to something else like admin@xxxx, helpdesk@xxxx, sales@xxxx.com

2

Yep, you can change that:

System Settings -> Virtualmin Configuration -> Actions upon server and user creation : From: address for email sent by Virtualmin

3

Out of this topic.

Besides sending a email notification to the server’s owner, could it be cc the same email notification to another email as a reference copy automatically ?

4

Yes: System Settings -> Server Templates -> Mail for Domain : Also Cc email to / Also Bcc email to.