Hello Maggot
Welcome to Poms in Oz.
1. As long as you are OK now, your medical history will not prevent you from obtaining Permanent Residency in Australia. The consultant who has now signed you off would probably have to do a report for the Medical Officer of the Commonwealth, after re-examining you at the MOC's request. However as long as your consultant is happy, there is no reason for the MOC (a GP) to be concerned.
2. In addition to the firm whose name has been filtered out automatically (which, you will find, happens on the British Expats forum as well: wwww.britishexpats.com) I would suggest that you contact several more Agents before attempting to settle on one of them. A lot of our Members speak very highly of Go Matilda, Ian Harrop & Associates, George Lombard and others.
http://www.gomatilda.com/news/index.cfm
http://www.ianharrop.co.uk/
http://www.austimmigration.com.au/site/?q=node/6
Best wishes
Gill