Quite good. If you can maintain a distinction average over your first year I can't see that you'd have any major difficulty applying for an internal transfer. I believe they consider a combination your WAM (weighted average mark) and your ATAR when deciding whether to permit the transfer. At least that's what they did when I transferred to UNSW after at year at Newcastle, anyway. It might be an idea to contact student central and ask directly, though.
The six compulsory core courses for B Economics (ACCT1501, ECON1101, ECON1102, ECON1202, ECON1203 and ECON1401) are also core courses for BCom/BEc so they'd transfer straight over. It would also pay to take MGMT1001 in your first year so you'd get credit for that as well (as it's a core for BCom/BEc). Then I suggest you take one of ACCT1151, FINS1613, INFS1602, LEGT1710, or MARK1012 so that every course you take in first year would be credited as a core course for BCom/BEc.
This way, as long as you get the required marks to succeed in a transfer, you wouldn't be behind at all in terms of time or money had you simply jumped straight into BCom/BEc.