score:4
If we have a look at the "what can you do" section of the 651 (link https://immi.homeaffairs.gov.au/visas/getting-a-visa/visa-listing/evisitor-651) it reads
Your eVisitor lets you: enter Australia for up to three months during each visit during the 12 months from the date the eVisitor is granted
So this seems that you can visit Australia for the next 12 months (the 12 months start the day the visa is granted); BUT you can stay there for only 3 months every time you go there.
If you're not married and plan to go alone have a look at the 417 too https://immi.homeaffairs.gov.au/visas/getting-a-visa/visa-listing/work-holiday-417