Start from what you have already done
Your intermediate stream is the hardest constraint in the whole system, and it was mostly decided at sixteen. Pre-Medical opens medicine, dentistry, pharmacy and the allied health degrees but closes most engineering routes. Pre-Engineering and ICS open engineering and computing but close medicine. I.Com and FA lead to business, law, media and the competitive examinations.
Some of this is recoverable — deficiency courses, equivalence through IBCC, and a few programmes that accept more than one stream — but recovery costs time. Work out what is genuinely open before you fall in love with a route that is not.
The mistake this prevents: Choosing a career first and discovering afterwards that your stream does not qualify you for it.