Bit of advice, as a commercial pilot it's a good idea to know where things are on the CASA website and in the CAR's and CAO's. You can't be expected to memorize it all but a bit of initiative when it comes to finding things out (especially as an instructor) isn't always a bad thing.
But as everyone has said you start off as Grade 3 and can instruct in all sequences up to CPL but cannot send people on their first solo's. You can also issue endorsements that you hold and can train students towards NVFR if you hold the rating (although come end of year that may be changing along with a lot of other stuff). Also for your first 100 hours you have to be directly supervised by the CFI or a Grade 1 approved by the CFI.
If you are only using the instructing as a stepping stone and nothing else then it isn't for you. If you're ultimately wanting to go to the airlines then thats ok but your priority as an instructor is the students and the quality of training they are getting, not your hours. Instructing is a great first job and your knowledge will increase well above your average 150 hour cpl holder, just make sure you have the passion to pass onto your students.
Good luck I hope it all works out.
Kiwivator