Hi,
just personal experience - thought it might be helpful. I would take your job offer in UK first, gain some experience and then come over to Aus.
reason I say this as you need a job offer before you can become registered, it’s really difficult to find an employer who will take you on prior to having registration.
i worked for a couple of years in uk first, and believe my experience is why I was offered work. Would have been a lot harder as a new grad as competing against Australian new grad OTs who also have registration. From what I’ve heard from students here it’s competitive.
good luck!