ATAR Notes was more than sufficient for me. Float your name around on the boards of subjects you're tutoring in, and gradually you'll get requests coming in throughout the year.
Also, if you have a relatively wide family/ family-friend connection base, use that to your advantage. I'm now at the stage where I'm convinced everyone knows someone who knows someone who's doing Year 11/12 (or younger year levels if you're prepared to tutor them as well - often less pay, but less strenuous too.)
If you find yourself struggling to pick up any students, perhaps print off some business cards and drop them off in your local area. I was considering doing this just at a few local shops and places I used to work at (conveniently located within walking distance of about 3 different schools

) but after a while I found there was enough demand elsewhere.
I'd also agree with Ned that there's not much point in study plans before you know your students. Obviously you're wanting to bring them up to the highest possible standard - most people have the 40+ benchmark as their rough goal - so your content will be geared towards that level, but there's a huge variety in skill level across the board. A few of my students last year were simply looking to
pass English; something they thought impossible early on. Others, meanwhile, wanted to maximise their chances from a ~45 to the very high 40s/50 territory. So there were occasional concepts that I would teach everyone, albeit in different ways, but for the most part I had to adapt to various different skill levels and learning styles quite quickly.
You can (and probably
should if I'm honest) plan ahead and have some possible activities or exercises set out in case you need them, but you don't want to get too dependent on these. Imo the most effective tutoring is done when you ask a student 'what don't you get about this unit/question/concept,' getting them to pinpoint their areas of weakness, and then you going through a bunch of explanations and strategies with them.
What subjects are you thinking of tutoring, if you don't mind me asking? And is there a reason you're set on waiting till next year?