Hi there
I did Art back in 2013, and to be honest the theory aspect really wasn't difficult. Familiarise yourself with the format and content of exams early on and you should be fine. The short answer questions are just stock visual analyses with occasional commentaries or framework guidelines to direct your discussion, and the "essay topics" are usually something to the tune of 'write about stuff you learnt this year.'
Each school organises SACs differently so I can't say much there. It might be worth pestering (nicely!) your teacher for more information; I really regret not doing this since my teacher gave us little to no warning about the date of the assessment, let alone the task.
The practical component is definitely more important and time-consuming, and my best advice there would be do start finalising your folio a week or more before it's due. So many people (myself included) leave it till a few days before to actually collate annotations and put everything together. If your luck, the folio will be due at a time when you don't have a pile of other SACs to wade through, but if your teacher schedules it during busy weeks, you don't want to be cutting and pasting while revising for methods tests and english essays. The more work you do early in the year, the easier time you'll have closer to the due dates.
Re: mark breakdown, from what I gather, prac and theory are 50/50 each, but the folio is worth 40%, your final pieces are worth 10% (but these are mainly judged by the quality of your folio anyway.) SACs are 25% and the exam 30% - whether this has changed, or varies from school to school I can't say. (VCE Art is not one of the better organised subjects
)
If you're really worried about theory feel free to post questions. I wouldn't stress too much though. Provided you're a competent writer and have a good bank of art terminology to draw from, it's just a matter of practice