can i have more than one e mail open

If you mean can you be writing two or more different emails or have to or more email open to read, the answer is yes. If you mean you want more than one Window Viewer (the window that shows the list of emails and mailboxes) I think the answer is no, at least I can't make more than one be open.

Yes. You need to not be in full screen mode. If you want two "viewer windows", where the list of messages is displayed, you can do it via "New Viewer Window" in the File menu or via the control-click menu on Mail in the Dock.