No contact from the seller isn't necessarily too much of a concern, as long as they post the item promptly etc, but if you've sent direct messages that require a reply, then I may be concerned. For me, it first depends on the item and then the seller's location.
You mention that they were a new seller and the item is worth hundreds of dollars - did you pay well below normal retail? Unfortunately, it's all too common for new members to list desirable and expensive items at a too good to be true price, and that's exactly what they are - too good to be true. (The items don't exist and the intent is to farm for information, which they get when people buy/pay, and take any cash they can along the way).
If you don't think the above applies to your purchase, then in general I'd give the seller about 2 days to respond to a message, and/or around two weeks for the item to arrive if posted within Australia, 3-5 weeks if being sent from overseas.
You have up to 45 days to open a claim with PayPal (best to open no later than day 44, as it's to the minute of payment), and once opened, if it's not resolved, you then have up to 20 days to escalate it to a claim.
