Re-entry into the US a few days apart on two different visas

Funny situation here:
I'm going to attend a conference in the US at the end of September to which I intend to travel using the VWP (Aussie citizen). In parallel, I initiated the process to obtain a J1 visa. It is (very) unlikely that I'll be able to get an appointment at the US Consulate General for my J1 visa and get my passport back in time to attend the conference, so I'm going to take the safe option to schedule an appointment once I return from the conference.
My question is:
Can I legally fly to the US for 5 a day visit (conference) as a tourist then fly back to Australia to get my J1 visa added onto my passport and travel back to the US straightaway? Or do I have to remain out of the US for a certain amount of time before travelling back? I don't expect to remain in Australia for longer than the time it'll take my passport to be sent back to me, which I understand is on the order of 10 working days.
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How often can I travel to the US on a tourist visa?
There is no limit on the number of times you may enter the U.S. under either ESTA of a visa. However, if reentering the U.S. using ESTA soon after staying for nearly 90 days, you can expect to be questioned in detail by the immigration officer about the purpose of your visit.How long do you have to leave the US before returning?
There is no set period you must remain outside the USA before returning but: "When traveling to the U.S. with the approved ESTA, you may only stay for up to 90 days at a time - and there should be a reasonable amount of time between visits so that the CBP Officer does not think you are trying to live here.How long can you visit the US from another country?
The Visa Waiver Program (VWP) enables most citizens or nationals of participating countries* to travel to the United States for tourism or business for stays of 90 days or less without obtaining a visa.When can I return to the US after 6 months stay?
Maximum Period of Authorized Stay Therefore, a person who stays for six months and, instead of applying to extend their visit inside the U.S. if they are a visa holder or a Canadian, departs and attempts to return to the U.S. in less than six months from the departure date, will be barred from re-entry for six months.BEING LEGAL IN THE U.S EVEN AFTER YOUR VISA EXPIRES
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Images: Brett Sayles, Karolina Grabowska, Karolina Grabowska, Karolina Grabowska