Unfortunately you heard or read wrong, never heard of a 5 year ED visa and secondly it's not that easy to start a business in Thailand like everyone thinks.also you can't own land in Thailand, but you could buy a condo. Best advise I can give come for a few months and look at your options once you are hear. If you are eligible you can get a TR 60 multi entry visa.
maybe you posted to Canberra embassy but Sydney consultant its been like that for years. Nothing new, the reason you got it all sent back is you didn't do it online like they ask. Like I said follow the instructions and you will be fine.
you have always if applying to the Sydney consult, had to apply online and wait for them to approve and and receive an email, saying send your stuff lol If you follow the instructions there should be no problem. The visa itself is a invite to visit Thailand. This is nothing new.