keeping assets 'unencumbered'

I have been having trouble wanting to sell our principal place of residence and buy land and rebuild
The BOM seem to have me in a prety good position
I have 350K borrowings with them and they have my PPOR and the IP title

They are not interested in the commercial title I have which is unencumbered

Even though it is in the Manchester Unity Bld CBD Melbourne and been tenanted for the last 15 years

I was looking at doing a course with Steve Navara and one of his sessions is maxamising borrowings while keeping asets unencumbered

Is there any one out there that can throw some light on this as I have found a block with an old house on it and want to make an offer

Part two of the question-If I buy and use as a renter for 2 years can I then demolish and build a new home having had the benifits of depreciation and the other tax benifits

Any help is appreciated regards Frank