Tourist visas for Poles are free, but all others are expensive. For example, a professional permanent residence visa for a family of four is over $ 8,500. The partner visa is $ 7,850. More information can be found here: https://immi.homeaffairs.gov.au/visas/getting-a-visa/fees-and-charges/current-visa-pricing

Information on this is available on the immigration department website https://immi.homeaffairs.gov.au/visas/getting-a-visa/visa-processing-times/global-visa-processing-times

Time estimates of waiting for individual visas often change and are given not precisely – over a wide time range. Indeed, for example: partner visas are sometimes processed within six months or even less, but often it takes more than one and a half years.

A tourist visa of subclass 651 is issued for twelve months, but you can only stay for three months after each entry. Other temporary visas are generally granted for a period appropriate to their purpose, although a time limit is used in many cases, for example, some work visas have a four-year limit and others two. Please note that permanent resident visas are valid for travel and return to Australia for only five years, although they allow you to stay in Australia forever

No, it is impossible

You should never, never allow this to happen. Remaining in Australia after the expiry of the visa may be subject to deportation as well as a ban on another temporary visa in the future. If you find yourself in such a situation, seek professional advice immediately from an immigration attorney’s agent or attorney

A visa is required for all professional, work, student and Work and Holiday visas. It is not required for family and tourist visas