1. Why do you want to wait till you reach Oz before applying for a Student visa, please? Wouldn't it be easier and cleaner to get the Student visa whilst you are still in the UK?
2. Which visa do you intend to use in order to be able to enter Australia in the first place? Visitor visas are not supposed to be springboards to anything else.
3. Does your 46 year old Partner have any children of his own, please? If not, or if his children do not upset the Balance of Family Test, I would suggest the following strategy:
A. Apply for the PV 103 for both of you, with you as the main applicant for that, without delay. It would take the PVC (Parents Visa Centre) about 6 weeks to acknowledge recipt of the PV application and to confirm that they have added it to their system.
B. Once you get the acknowledgement from the PVC, then apply for a Student visa for your Partner, with you as his dependant. The academic year begins at the end of Jan/beginning of Feb in Australia, so there would be plenty of time to do things this way around. He would want to enrol for a course that begins in late Jan/early Feb 2013.
You would not need specific Permission to Work. That is now granted automatically with Student visas.
Whether or not you really need a migration agent to help with any of this depends on you more than it depends on anything else. If you are prepared to do some head-banging until you understand all the relevant words on the DIAC website, plus you are prepared to be really thorough and conscientious about getting all the paperwork right, there is no reason why you shouldn't deal with both visa applications by yourselves. It is not rocket science, DIAC provide an extremely helpful Checklist with every type of visa, which you can download from their website, and DIAC really do simplify the process and make it easy for any applicant in person who is not an unreliable scatterbrain.
A Registered Migration Agent in the UK would charge you about £600-£800 (possibly plus VAT) for dealing with an application for a Student visa. They'd probably want somewhere in the region of £1,000 (+/- VAT) for a PV 103 application. I'm dubious about the value of that, myself, when there are no complications and all that it needs is for you yourself to keep a cool head and to do it methodically, one visa at a time.
Don't try to prepare both applications at the same time - it would be much easier to cut your teeth on an application for a PV 103 - which are as ridiculously simple as it is possible for them to be, bearing in mind that the Forms were designed by bureaucrats with little common-sense but plenty of zeal! Once you've despatched the PV 103 application, then you can clear your desk and make a start on the nuts and bolts for the Student visa application next. Just by wading through the extremely tedious but actually very straightforward procedures for the PV 103, you will learn how DIAC's mind works, if you like.
FWIW, my own mother has a Contributory Parent Visa sc 143. In 2005, I discovered that she would be eligible for a CPV. I then discussed it all with my sister Elaine, who has lived in Perth since Noah was a nipper. I happen to be a solicitor in England & Wales but I had never dealt with any Immigration Law matters, didn't study Immi Law as an optional extra or anything and to start with, I was totally baffled by the DIAC website as it was at the time in 2005 (2 websites before the current one.)
I couldn't understand a word of it, to begin with. I had never come across Immigration Jargon before, didn't really understand what a visa actually is, legally, didn't understand the concepts involved in Immigration and so forth. Having discovered that Mum would be eligible, I told Elaine that I supposed the next step would be to find and instruct a migration agent? Elaine said, "Waste of money. If you're sure that Mum is eligible then we can do the application by ourselves." She turned out to have been 100% right.
PS: Precisely because I'm a lawyer and I was scared sh*tless that I might make a mistake, I beat my own brains into a much finer pulp than was either actually necessary or most people would do! My own imagination was making the whole thing seem much hairier than it actually was/is!
PPS: There was a potential BoF Test complication for my Mum. She has a step-child as well as two children of her own and only one of the 3 lives in Australia. The old DIAC website contradicted itself. One of the Fact Sheets said that the step-child wouldn't be counted in the BoF Test. The other Fact Sheet said that she would be. There was nothing to indicate which of these two Sheets was correct.
So then I downloaded the legislation itself, to have a squint at what the relevant Law actually said. I became convinced that the Australian Government uses kangaroos as Parliamentary Draftsmen. Canberra is full of roos, apparently. I reckon that at least 50% of them are on the Federal Government's payroll and that they are not being paid just to mow the grass with their teeth!