I'm pretty sure for science/law first years, you take 3 science and 1 law subject. Or at least that option's available to you. There's no number of law subjects you HAVE to take in any particular year. Just enrol in whatever you want and you'll get your degree once you've completed the requirements.
That said, the two first year law subjects you'll do is NOTHING like what the rest of the course is like (it's basically an introduction to legal reasoning, writing and research. Also statutory interpretation, history of the common law system, the structure of the legal system in Australia etc.)
So it's not going to be a good indication of whether or not you'll enjoy law.
Also re: tute sizes - in the LLB they're like 25 people. It doesn't sound like much but when your tute marks depend on how much you're contributing to the discussion, having to compete with 24 other people who also want the full marks gets a little... tiring.
Lecture sizes can be anywhere from 50 - 200. That's why we have tutes and consultation hours so you can ask questions without the rest of the class wanting to shoot you in the face for wasting their precious time.
After thinking about it more, I've realised that I'd really be pursuing law to keep my options open - it's closely related to a field that I'm very interested in
That's what I would say at least 1/3 of law students (including myself!) are doing

(i.e. keeping options open). Nothing wrong with that.