With regards to training material it is probably a mixture. I have been asked to run some workshops for the learners and I am creating my own resources but for the main units they are studying we have pre-prepared training materials purchased from an external source.
It is important to get the Cert IV TAA or else you will struggle to even get an interview unless it is a particular area they have a shortage in and will be willing to take you on while you studying for it.
In my case, I had the TAA qualification and additional qualifications, the work experience and was in the right place at the right time, I spotted the advert on a Friday and applied more or less as soon as it came on seek.com.au and they rang me a few hours later to come for an interview on the Monday and I started on the Thursday.
I have to add I have been here just over 3 years now and it has taken this long for things to start slotting into place workwise.