You do not have to choose a major yet, in the first year you do the prescribed core courses.
See the UNSW Business school website: https://www.business.unsw.edu.au/Students-Site/Documents/Commencing-Actuarial-Enrolment-Guide.pdf for enrollment recommendations.
1) You can transfer by doing just commerce, only you need to do 2 math courses (which can count as gen ed courses).
2a) You could do a combined degree commerce/science and do the math courses as part of your science degree...
Yes, the courses you will do to get exemption for part I in this degree are:
CT1: ACTL2111
CT2: ACCT1501 AND ACCT1511 AND FINS1613
CT3: ACTL2131
CT4: ACTL2102 AND ACTL3141
CT5: ACTL3151
CT6: ACTL2102 AND ACTL3162
CT7: ECON1101 AND ECON1102
CT8: ACTL3182
Those courses can be done in the first...
Not true. UNSW provides more flexibility, e.g. double majoring in single degree, combined degree allows for part 2 exemptions, double majors. Accounting/Finance at UNSW is in top 10 worldwide link including employers reputation (which makes you get a job). So the actuarial curriculum is similar...
Yes, you are right for typical UNSW graduates. Because they double major they are very likely to get a decent to good job in the financial industry.
When you get your professional exemptions you are likely to find an actuarial job. In case you don't, or figure out that actl is not for you, you...
Note that at Macquarie link the bachelor degree in itself does not provide you with all the exemptions for part 1
"Students with grades of credit or better in the relevant units may earn exemption from Part I of the examinations of the Institute of Actuaries of Australia. To complete all of...
Differences between the programs at Macquarie and UNSW are due to the difference in ATAR for entrance in the courses. At UNSW the ATAR for commerce degrees are 96.3 link, whereas at Macquarie the ATAR for commerce is 81 link. Thus at UNSW in all courses you are in a class with smart students...