Yeah got the call on Friday too! Have my application status sitting on "Complete Class III Medical" like Bennett.
I'll admit I already got my Class 3 sorted
, but in hindsight I think I got a little excited with wanting to get everything on my end sorted and out of the way.
I'd say wait until they give you the go to get started - there's plenty of time still, and you don't want to be sitting and wasting approximately half a year of the 2-year validity period (I'll likely have to renew around the end of the course). The medicals are thorough, though not as stringent as that for pilots as far as pre-existing conditions go.
The news so far is that our batch (which at AC was told would start in Aug) is likely to make a start early 2016 (probably Jan), and even the batch in June had to be apparently moved up to October this year.
All the best to candidates in whichever phase! It has and will be a very long process indeed.