Have a similar query. We are looking to move from our current PPOR due to work relocation for hubby.
We have been planning to sell this, buy another PPOR and then look at purchasing an IP, so have been busy getting this ready for sale. 
Current situation:
PPOR value  $550K
Shack value  $150K (maybe more?)            One LOC @ 6.01%, $235K outstanding
We receive some tax benefits for the shack as an IP for interest on around $120K and repairs/maintenance etc and minimal income

New PPOR purchase price: $500K plus costs $25-$30K
New IP value unknown, but thought around $350K + costs

Just attended a short property investment course information session which suggest that the golden rule is never to sell.  It gave me food for thought.  A quick search suggests our current home may rent for around $450-$500 week.  It is large and about 35 years old (although we have maintained it well) so I'm not sure that its an ideal IP, but just trying to get a feel for options.

Any advice would be much appreciated before we go to the expense of involving taxation advice etc.

Thanks