would need to be at 2000agl then descend to 500 agl through two circuits levels on upwind
That's why you
do descend on upwind; you're not yet in the circuit.
Would you get Hi-Perf aircraft at YTOC? If not, that's one layer removed. Now it's only a descent from 1500ft.
6.6.4 of the CAAP does suggest joining at 500ft crossing the runway at midfield. At YTOC, whether that implies you could join on upwind ie along the runway at 500ft is another thing. Lots of potential conflicts: aircraft/gliders turning final belly-up to you (from both directions) and taking off and doing go-arounds (oh and those jokers doing Straight-ins, too)!
May be better to position well outside of the circuit and then just join on downwind at 500ft (as suggested in ERSA). For at least 180° of inbound tracks, that would work OK.
And of course, Talk... A quick call will direct your eyes and you can then keep clear of others.