1. Do as many practice exams as you can, work out where you make errors and put them in an errors book (with the correct answer/method too) Look through that book all the time, add any recurring mistakes into a section in your bound reference. Make sure you can use the CAS well and you know the functions that are normally needed. Watch edrolo on any topics you're unclear about or make a lot of mistakes in. Do checkpoints questions as well as practice exams, but prioritise practice exams.
When it comes to the bound reference, make sure it has everything in the course (obviously) - you should never have to use it but even the process of writing it is good revision. Add a section with common errors like I said before but also add a section with hard examples (any hard questions you came across in your exams, checkpoints, textbook, ) just in case you need it.
2. Realistically you could do company exams in any order, the main thing is to leave the VCAA exams (esp. the latest ones) to around the end since they obviously give you the most accurate idea of what's on the actual exam.
3. Personally I would stay away from doing whole exams from the old study design, and instead choose questions from them that are 100% relevant. But if you do want to do them, you could either compare the study designs to see what isn't relevant anymore, or just look at a question and see if it has any stuff from the old study design, and if it does just don't do it.