i reckon it would take a bureaucracy bigger than centrelink in order to fund this scheme

Funding refers to the dollars required. Bureaucracy refers to the white-collar government jobs required to keep track of the dollars.

Bureaucracy costs money. A UBI exists in part to render costly bureaucracy unnecessary - everybody with a tax file number receives it, so it can be handled by one database attached to the department of finance or the ATO.

<lots of words detailing why it won't work>

It is monumentally easier to dismiss new ideas than it is to champion them. The status quo will support you in your reticence.

It would be just as easy for me to come up with bogus ad hoc accounting to support my argument as you've done here, and it would be just as useful. What's important at the moment is the idea itself, and the fact that it is supported, mostly in spirit, by a handful of economists, pundits and the general public. Big changes can be wrought for the benefit of everyone, but they need champions at the beginning who will push past their inertia to at least keep an open mind. Just the idea of wiping out multiple levels of government, with the associated elimination of cost and intrusions into private affairs that entails, should attract many people. Just the thought of making personal dignity a human right should be enough impetus for most people.

in lieu of receiving UBI welfare

UBI is not welfare. It's another way to structure the finances of the nation. From a purely mechanistic point of view, transfer payments of this sort have the potential to make markets work more efficiently by employing unproductive national resources. If a different cognitive framework is required for you to accept this, perhaps consider a UBI as an investment in future microbusinesses. For ~$15,000 a year per business, we can be venture capitalists for the future of Australia's economy.