There is no conflict or separation between applying for Australian universities and the mainland. The admission information you want is clearly written on the website of Australian universities, in the column of registration office. Applying for an Australian university and volunteering are separate and will not affect admission to the Mainland.
If you want to use Australia as a springboard, that's fine, but it's better if you finish your undergraduate course and then go to a good foreign university for a master's degree, so you won't waste time, you won't go to a strange place at once (business English teaching, national textbooks), and you may not be able to transfer to a good school if you want to transfer. Unless you are outstanding in your freshman year and your English is super strong, don't talk about it. Anyway, you do. All the enrollment information is clearly written in the column of registration office, including the scores of previous years, but those are only the minimum admission and average admission scores. If you can score about 30 points in this line and Shandong Province, you can only apply for some less popular majors, business, especially accounting and finance, and reach about 80 points.