in case you haven't seen it - https://www.raa.asn.au/learn-to-fly/ gives the basics, have a browse. You wouldn't be able to fly out of Moorabbin or other controlled airports with only the recreational cert. Lots of threads on here about that.
i wouldn't say the theory is "simple", but certainly achievable by almost anyone with a passion for it. I think a couple of lessons first would be great, as the theory really comes to life when you can relate it to something you saw or felt or did. But resist the temptation to just think this is something you are going to knock out when you have the time. It becomes a way of life, there'll ALWAYS be something to learn or a test to prepare for - so think of it as a long term lifestyle... yes you can get it done more or less quickly but don't make that the point :) You won't be less of a pilot if it takes you 2 years vs. 1 year.. its for LIFE!
A sample question for the pre-solo might be something like - who has to give right of way in a given scenario. Or, what do such and such runway markings mean. They aren't difficult, or even really focused on aeronautical knowledge - your first solo will just be a circuit or 3 around the aerodrome, so they just need to know you have the "rules of the road" down so to speak. The finer points build on that and come later.
how often? as often as you can. Lots of memory and motor skills, which get lost after too much time - then you spend half of the next lesson (and $$) trying to get back to where you left off. that may not be feasible now, as happyflyer said, make year 12 your priority - do that right, and most everything else falls into place after that (well, more so than if you don't...).
welcome to the forum btw!