The Verdict: Clear Path
Your citizenship and age fit the working holiday agreement, so you can apply. Book an appointment at the Czech embassy or consulate for your country, early in the year if your quota is small.
The visa allows up to a year in Czechia, with work incidental to the travel. Only the Australian visa can be extended, and only to a year in total. It does not convert to another permit and does not count towards permanent residence.
Apply in person with your passport, proof of funds, medical insurance and a criminal record declaration. The fee is CZK 2,500 under most agreements, CZK 3,000 for Canadians, and nothing for Japanese applicants. Dependants cannot come with you, except under the Japanese agreement with visas of their own.
If you might stay longer, plan it during the year. The digital nomad programme excludes anyone who held a Czech long-term visa in the past year, and this visa is one, so take them in the right order.