Preparation is definitely the key. The exams are a mixture of CPL and ATPL as you can bypass the 16 CPL/IR exams and do the ATPL. VFR and IFR comms are a giveaway if you do the feedback papers. The exams are not that hard individually, it is the volume of them,you end up sitting 7 and 7 or 8 and 6 to complete the 14 exams depending on where you do your study. I can't recommend Bristol GS highly enough. I did my distance learning through someone else whilst still in Australia and did my 2 week brush up courses with them and that's what got me through all of them first time. The cost overall is enormous and don't forget the flying training.
For the IR conversion you can do most of it in a sim but the aircraft (PA34) was 350 pounds an hour and the IR test fee is now 695 pounds i believe!!! Convert that to AUD and you will cry. Also there might be delays for weather for CPL conversion in the winter. If you want an air taxi/charter job make sure you look at he hour requirements of the CAA. They even charge an extra 95 quid to put single engine aeroplane on your multi CPL/IR licence. My estimates were way under what it all cost but it was worth it in the end. Remember also, if you fail one exam 4 times you loose all your previous exam credits and have to start again. PS don't agonise over how to do a compass swing too much (as I did) as they don't actually test it.