It is very hard to determine whether what you should study which may be suitable for migration upon completion of your Australian studies given that migration rules are keep changing. We suggest that you contact us and we advise you based on your personal circumstances.
The processing time varies depending on the type of visa you apply for, for instance student visa applications are usually finalised within 1-3 months, partner visas within 12-15 months, permanent employer sponsored visas within 6-8 months from the date of lodgment. Have a look at the service standards of the Department for more information HERE
Migration to Australia / Visa to Australia / 457 visa / Skilled visa / RSMS visa / State sponsorship / Student visa - Open Migration