Because you chose to post this in Backcountry Beginners, I must assume you are fairly new at backcountry backpacking. You also indicate you intend to cover from 250 up to 350 miles of trail in "about two weeks", which would amount to from about 20 to 25 miles a day. That's not including any days off-trail for resupplying yourself with food, so your actual daily miles would probably be higher.

This is very ambitious for an inexperienced hiker, unless by "explore" you meant something other than a continuous hike of the entire 250 to 350 mile section. My first recommendation would be to scale back your ambition a bit to something closer to 15 or 16 miles a day. That would be more like a 200 mile section, with a few off-trail days interpolated for resupply. You can always enjoyably fill an extra hour or two each day with lounging about or side trips, if this mileage goal proves to easy for you.

The other thing I noted was your time frame will be in June. The higher elevation mountains of the western USA are often covered in residual snow from the previous winter in June, and this includes the most scenic parts of the PCT. You will either be walking on snow much of the time, making both walking and navigation difficult, or you must choose a lower elevation and somewhat southerly section, likely to be less snowy. This may not be quite what you had in mind.

Lastly, have you given much thought to your equipment? Will you bring it from Australia or plan to acquire it in the USA? The best way to cover lots of daily miles is to have a light pack. Beginners rarely have the experience to know what to bring and what to leave behind. We can help with that, too.

Could you clarify some of these issues for us, so we can more easily give you the advice you are seeking? Thanks!