I spoke to fellow Bulgarian who flew with Singapore Airlines. He entered just his First Name and Family Name and flew without any problems.
He didn't fly to Australia dough. My eVisitor visa consists of:

Given names: First name Middle Name
Family name: Family Name

And SQ say on their website:

Under Australia's Advance Passenger Processing (APP) system, visa information is obtained from all intending overseas travellers (except New Zealand citizens) and is available at airports before passengers arrive.
For successful Australia Advance Passenger Processing clearance, please make sure:
•The name that you used when making a booking to correspond with your passport name; and
•You have a valid electronic visa from the Australian Government's Department of Immigration and Multicultural and Indigenous Affairs

I know I may be panicing too much and everything will be fine with only First and Last name, but just want to be sure. It will be painful to be denied boarding in Singapore. The whole trip will be ruined.